My Gigabyte B650 motherboard boots straight into firmware settings after a shutdown. It detects the drive with Linux Mint 22.2 and the separate Windows 10 drive, but neither operating system appears as a boot option.
I'm looking for my Mint USB and don't have another PC available. Where should I start?
Since both boot options disappeared at once, I'd check the firmware settings before assuming both installations broke. Look at the boot order and whether the machine is set to UEFI or legacy boot. If that setting changed, it may no longer show entries created for the other mode.
Don't change storage settings or reinstall anything yet. Note the current settings first so you can put them back if a change doesn't help. The drives showing up means they're detected, but it doesn't tell you whether their boot partitions are intact.
Finding the Mint USB would be the most useful next step. Boot its live environment, then use Boot Repair to diagnose the boot setup. Review its report before applying repairs, especially with Windows on a separate drive.
I'd avoid running grub-install blindly. The right repair depends on how the system was booted and which EFI partition belongs to the installation.
The Windows installer USB can get you into the Windows recovery environment without reinstalling Windows. You can look at the repair options there, but hold off on changes until you've checked the firmware boot settings and have a clearer idea of what's missing.
If the Mint USB stays lost, a phone with USB OTG might offer a way to prepare a bootable drive, depending on the phone and available tools. Ventoy or Super Grub2 Disk may also help find and boot an existing Linux installation, though getting a tool onto USB is still the hurdle.
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iNsertCoinLater:
Making boot media usually erases the target USB drive, so check its contents first. Booting Mint this way would help with diagnosis, but wouldn't necessarily fix the missing firmware entry.