NOT SOLVED. I am using Linux Mint 20.2, with a Cinammon Desktop.

Synaptic would not launch from Menu.
I tried a reboot, but it hung up at a Console terminal asking for a Login.
This result repeated several times.

After a fresh install of Linux I did sudo apt install LXDE.
I logged into LXDE; and there Synaptic launched from the Menu.

I logged back into Cinammon; did a reboot, and got that same Console Window.
I tried this again: with the same result.
Opening synaptic somehow causes this problem.

Having learned my lesson, I reinstalled Linux; but this time I will not try to launch synaptic, from either the Menu, or the xterm.
Instead I will install a program with ‘sudo apt-get install xxxxxx’

So you worked around the problem. Nothing wrong with that, but an actual solution exists. A Quick Search(tm) leads me to a Mint Forum thread, start reading here.

Before you read this I want you to know that synaptic will not launch from terminal.

I went to the thread, and did all of the commands:

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ apt list *policykit* --installed
Listing... Done
policykit-1-gnome/focal,now 0.105-7ubuntu2 amd64 [installed]
policykit-1/focal-updates,focal-security,now 0.105-26ubuntu1.1 amd64 [installed]
policykit-desktop-privileges/focal,focal,now 0.21 all [installed]

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ ls /etc/xdg/autostart | grep polkit
lxpolkit.desktop
polkit-gnome-authentication-agent-1.desktop
polkit-mate-authentication-agent-1.desktop
edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ ls ~/.config/autostart
dbus-session-addr-save.desktop LXinput-setup.desktop
dbus-session-addr-save.sh plasma-netbook.desktop
dropbox.desktop 'ProtonMail Bridge.desktop'


I then went to the ‘Quick Search’, under SOLVED, and did all of those commands:

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ id
uid=1000(edhe) gid=1000(edhe) groups=1000(edhe),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),114(lpadmin),134(sambashare)

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ sudo dpkg -C
[sudo] password for edhe:

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ sudo dpkg -V
??5?????? /usr/share/applications/libreoffice-math.desktop
??5?????? /usr/lib/firefox/browser/defaults/preferences/vendor-firefox.js
??5?????? /usr/lib/firefox/distribution/distribution.ini
??5?????? /usr/share/applications/libreoffice-draw.desktop
??5?????? /usr/share/applications/yelp.desktop
??5?????? c /etc/dhcp/dhclient-enter-hooks.d/resolved
??5?????? /usr/share/icons/gnome/16x16/places/debian-swirl.png
??5?????? /usr/share/icons/gnome/22x22/places/debian-swirl.png
??5?????? /usr/share/icons/gnome/24x24/places/debian-swirl.png
??5?????? /usr/share/icons/gnome/32x32/places/debian-swirl.png
??5?????? /usr/share/icons/gnome/48x48/places/debian-swirl.png
??5?????? /usr/share/icons/gnome/scalable/places/debian-swirl.svg
??5?????? /usr/share/icons/Adwaita/16x16/places/start-here.png
??5?????? /usr/share/icons/Adwaita/22x22/places/start-here.png
??5?????? /usr/share/icons/Adwaita/24x24/places/start-here.png
??5?????? /usr/share/icons/Adwaita/32x32/places/start-here.png
??5?????? /usr/share/icons/Adwaita/48x48/places/start-here.png
??5?????? c /etc/casper.conf
??5?????? /usr/share/initramfs-tools/scripts/casper-bottom/01integrity_check
??5?????? /usr/share/initramfs-tools/scripts/casper-bottom/15autologin
??5?????? /usr/share/icons/HighContrast/16x16/places/start-here.png
??5?????? /usr/share/icons/HighContrast/22x22/places/start-here.png
??5?????? /usr/share/icons/HighContrast/24x24/places/start-here.png
??5?????? /usr/share/icons/HighContrast/32x32/places/start-here.png
??5?????? /usr/share/icons/HighContrast/48x48/places/start-here.png
??5?????? /usr/share/icons/HighContrast/scalable/places/start-here.svg
??5?????? /usr/share/applications/im-config.desktop
??5?????? /usr/share/sounds/freedesktop/stereo/device-added.oga
??5?????? /usr/share/sounds/freedesktop/stereo/device-removed.oga
??5?????? /usr/share/cups/data/default-testpage.pdf
??5?????? c /etc/fwupd/daemon.conf
??5?????? c /etc/fwupd/remotes.d/lvfs-testing.conf
??5?????? c /etc/fwupd/remotes.d/lvfs.conf
??5?????? c /etc/fwupd/thunderbolt.conf
??5?????? /usr/share/applications/info.desktop
??5?????? /usr/share/applications/mate-color-select.desktop

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ ^C

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ sudo inxi -Fxz
System:
Kernel: 5.4.0-74-generic x86_64 bits: 64 compiler: gcc v: 9.3.0
Console: tty 0 Distro: Linux Mint 20.2 Uma base: Ubuntu 20.04 focal
Machine:
Type: Desktop System: Hewlett-Packard product: HP Compaq Pro 6300 SFF
v: N/A serial: <filter>
Mobo: Hewlett-Packard model: 339A serial: <filter> UEFI: Hewlett-Packard
v: K01 v02.90 date: 07/16/2013
Battery:
Device-1: hidpp_battery_0 model: Logitech K350
charge: 70% (should be ignored) status: Discharging
Device-2: hidpp_battery_1 model: Logitech Wireless Mouse M510
charge: 55% (should be ignored) status: Discharging
Device-3: hidpp_battery_2
model: Logitech Unifying Device. Wireless PID:1025
charge: 50% (should be ignored) status: N/A
CPU:
Topology: Quad Core model: Intel Core i5-3470 bits: 64 type: MCP
arch: Ivy Bridge rev: 9 L2 cache: 6144 KiB
flags: avx lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 25541
Speed: 1596 MHz min/max: 1600/3600 MHz Core speeds (MHz): 1: 1597 2: 1597
3: 1596 4: 1596
Graphics:
Device-1: Intel Xeon E3-1200 v2/3rd Gen Core processor Graphics
vendor: Hewlett-Packard driver: i915 v: kernel bus ID: 00:02.0
Display: server: X.org 1.20.9 driver: modesetting unloaded: fbdev,vesa
tty: 80x24
Message: Advanced graphics data unavailable for root.
Audio:
Device-1: Intel 7 Series/C216 Family High Definition Audio
vendor: Hewlett-Packard driver: snd_hda_intel v: kernel bus ID: 00:1b.0
Sound Server: ALSA v: k5.4.0-74-generic
Network:
Device-1: Intel 82579LM Gigabit Network vendor: Hewlett-Packard
driver: e1000e v: 3.2.6-k port: f060 bus ID: 00:19.0
IF: eno1 state: up speed: 1000 Mbps duplex: full mac: <filter>
Drives:
Local Storage: total: 931.51 GiB used: 16.97 GiB (1.8%)
ID-1: /dev/sda vendor: Western Digital model: WD10EZEX-08RKKA0
size: 931.51 GiB temp: 32 C
Partition:
ID-1: / size: 915.40 GiB used: 16.97 GiB (1.9%) fs: ext4 dev: /dev/sda2
Sensors:
System Temperatures: cpu: 30.0 C mobo: N/A
Fan Speeds (RPM): N/A
Info:
Processes: 204 Uptime: 14h 41m Memory: 15.52 GiB used: 2.27 GiB (14.6%)
Init: systemd runlevel: 5 Compilers: gcc: 9.3.0 Shell: bash v: 5.0.17
inxi: 3.0.38

synaptic-pkexec did not launch synaptic, and I will have to do another fresh install. But before I do I will try running a lens cleaner on my cd drive.

I tried right-clicking on the menu item but nothing appeared about ‘configure’; only Add to ..., or Uninstall.

I applied a cleaning disc to the CD Drive Lens.
I downloaded, and burned a new Linux Mint 20.2 disc. Verified.
I re-installed Linux with the new disc.
I am now waiting for your reply to my previous post.

I am not touching Synaptic. I am very tired of rebooting.

Note: I always see, during reboot: 'Integrity: Problem loading x.509 certificate -74'

edhe@edhe-HP-Compaq-Pro-6300-SFF:~$ synaptic-pkexec
Invalid MIT-MAGIC-COOKIE-1 keyUnable to init server: Could not connect: Connection refused
Failed to initialize GTK.

Probably you're running Synaptic on Wayland with root permission.
Please restart your session without Wayland, or run Synaptic without root permission

I followed a recommendation from a man at https://support.google.com/chromeboo...nd-issue?hl=en
I created a script named rgui:
xhost +si:localuser:root
sudo $*
xhost -si:localuser:root

./rgui synaptic-pkexec
localuser:root being added to access control list

(synaptic:96031): Gtk-CRITICAL **: 13:45:27.080: gtk_widget_hide: assertion 'GTK_IS_WIDGET (widget)' failed

and it works.

I just did a restart; and even though I never tried to launch synaptic from the menu; and only used ./rgui synaptic-pkexec; or sudo app ...; it DID NOT restart, but stopped at a Console window asking for a login!?

Help, please!

I have been waiting patiently for someone to revisit my post. What is causing my restarts too crash?

Could it be a BIOS problem?

Attached Thumbnails

     

I switched to Linux Mint 20; and I have a strong suspicion that a restart will fail.

HISTORY
About a month ago Linux Mint 20.2 was working fine.
I decided to try the recovery drive that I had from the Windows 10 Pro that came with my computer.
I had heard that it could reinstall the Windows 10 that I had erased. I had a dual boot going; but then Linux restarts continually ended in a Console login window.

I let the recovery drive go through a procedure of 'removing files'.
This ended with the message that Windows had encounterd an error; and it stopped.
Later, with GParted I found that Windows had lied; and that they had installed their system. It didn't boot though.
I left windows at that point; and from then I have had problem after problem with Linux Mint.
I thought of checking for any bad blocks - but that takes way too long.

Isn't the answer in posts #5 and #6?

Sorry, I don't use wayland.

And why BIOS? Your problem is an operating system problem, please leave the BIOS out of it.
edit: it is of course possible that your reboot problems have nothing to do with synaptic. Are you dual booting Windows, and still using it sometimes?