With dual boot I can no longer get into BIOS

I bought a HP-Compaq-8100-Elite-CMT; and it came with Windows 10. I added on Linux Mint as a Dual Boot. On Grub Linux and Windows appear as options. Only Linux will work. I read that if I went into BIOS and disabled Fast Boot, and Secure Boot, that Windows might start. However F12 no longer appears at the lower right hand corner; and as a check the HP description of this Desktop specifies that F12 is the BIOS key.
I tried shutting down the unit; and at restart either continue to press, or to hold the F12 key. I get the message:

Attempting Boot From IBa GE Slot 00CB v1353 (PnP Device)
Interl(R) Boot Agent GE v1.3.53
Intel(R) Boot Agent PXE Base Code (PXE-2.1 build 089)
Client MAC ADDR: 2C 27 D7 24 06 A0 GUID: 2DE89DBF 3699 E011 BBDA D72406A02
DHCP..../

Then it exits; without going into BIOS.

Has anyone had a similar experience.
I suspect that Windows is the culprit.

Maybe I was looking a the wrong technical guide, but the one I saw online said F12 is "Network Boot" - which makes sense with those messages.
Try F10.

or esc .. then its all the others F keys .. some fast boots you nearly have to have you finger already one the BIOS key when you press your power key else it starts up too fast.

Turn on the computer and immediately press the F10 key repeatedly until a BIOS Setup screen opens. If nothing happens, press the F1 key repeatedly. In the BIOS Setup utility, do one of the following: On the Main tab, find the BIOS version.

https://support.hp.com/us-en/document/bph07110

I am getting no where with the F keys; or ESC.
A friend recommended:
To check out rEFInd and download the usb image.
https://www.rodsbooks.com/refind/getting.html
He said that this works and looks a lot nicer than grub for UEFI systems; and to make a bootable flash drive by following the instructions.
I went as far as I could.
In the rEFInd README I saw this:
"Be aware that the disk image file uses GPT, and the GPT data structures are sized for the disk image, which is very small by today's standards. Thus, the backup GPT data structures will be placed early on the disk. Most OSes
cope well with this, but you may want to correct the problem if you want to use the disk for other purposes in the future."

I will use a new USB for this.

rEFInd README recommended "dd if=refind-flashdrive-{version}.img of=/dev/sdx"

~$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 931.5G 0 disk
├─sda1 8:1 0 350M 0 part
├─sda2 8:2 0 97.7G 0 part
├─sda3 8:3 0 9.8G 0 part [SWAP]
└─sda4 8:4 0 823.8G 0 part /
sdb 8:16 1 58.9G 0 disk
└─sdb1 8:17 1 58.9G 0 part /media/edhe/USB DISK
sdc 8:32 1 15.5G 0 disk /media/edhe/6126-4BCD
edhe@HP-Compaq-8100-Elite-CMT:~$

With no mention of Windows??

/Downloads/refind-flashdrive-0.11.2
-rw-rw-r-- 1 edhe edhe 7.3M Oct 22 17:03 refind-flashdrive-0.11.2.img


Is this the right command:
sudo dd if=/home/edhe/Downloads/refind-flashdrive-0.11.2/refind-flashdrive-0.11.2.img of=/dev/sdb1

jack that hdd out of your system give it nothing to boot with, then try your keys.

sudo blkid
to see partition types

$ sudo blkid
/dev/sda1: LABEL="System Reserved" UUID="7E88DA2288D9D8AB" TYPE="ntfs" PARTUUID="0f3f3740-01"
/dev/sda2: UUID="01D285E8BED961F0" TYPE="ntfs" PARTUUID="0f3f3740-02"
/dev/sda3: UUID="FC9AF6529AF608C2" TYPE="ntfs" PARTUUID="0f3f3740-03"