I've been dual booting Manjaro and Windows. Today Manjaro updated and I noticed that the grub menu wasn't there on boot; it just booted into Manjaro. So I went to try and fix grub, but when I run mkconfig it doesn't find Windows. I mounted the partitions before I run it. Not sure what else to do. I ran os-prober on it's own and it found Windows. Anyone can help me fix this it'd be appreciated.
Something else that may make a difference: I updated my BIOS firmware just before the Manjaro update came out. The computer was still booting normally after the BIOS update and before the Manjaro update. Not sure if some setting in the BIOS was changed that I'm missing or not.

EDIT: I also removed grub and installed it. No difference.

SOLVED: Nevermind. grub config file had os-prober diabled by default on the Manjaro update. Had to uncomment a line and then run mkconfig.

Exactly the same issue - os-prober is disabled for some reason all of a sudden
Haven't been able to fix it yet either.
Even tried Grub-Customizer, but it can't see Windows either.
finds it, but how do I then get that into grub?

EDIT 1: just saw your 2nd edit - will try, thanks

EDIT 2: Nope. Still booting right into Manjaro - and even Timeshift doesn't help

open etc/default/grub as root
find GRUB_DISABLE_OS_PROBER="false" and uncomment that line
save file
run grub-mkconfig -o /boot/grub/grub.cfg

worked for me.

Worked for me too, thanks.
EXCEPT
when I installed my VPN client, I had to do an update. And the update cleared the grub menu again.

So it's Manjaro.
My favourite distro, but I've had so much trouble with weird things since December, I'm dumping it. Again.

If this fixed your issue, should mark it as [SOLVED].

thanks

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this manjaro issue is all over (linux on) reddit.