[Solved] Installed Xanmod, and now Linux Mint can't boot and devices won't work

[Crigence]

Yeah, I know it was probably stupid to try switching to a unsupported kernel as a complete noob, but I like playing games on my Linux Mint computer and a few different videos said that the Xanmod kernel was better for that, so I accepted the risk and assumed that any damages could just be fixed through the terminal, which I had actually already had to do at that point.

So I tried installing Xanmod kernel through the official instructions listed on the website. Everything went fine, up until I noticed that for some reason,

sudo apt update && sudo apt install linux-xanmod-x64v3

wasn't executing the second part of the command, so I tried just executing

sudo apt install linux-xanmod-x64v3

on its own, and it seemed to have worked properly. After that, I restarted my computer, and now we're here.

The computer starts, and gets to "GNU GRUB." First thing I notice is that now all of my devices fail to start (Keyboards, mice, etc), so I can't interact with menus at all. After 30 seconds, it automatically attempts to boot into Linux Mint, which brings up a screen that eventually reads this:

error: bad shim signature
error: need to load kernel first

Press any key to continue...

Failed to boot both default and fallback entries

Press any key to continue...

Then, finally it boots me back to GRUB, which I obviously can't do anything with. An important thing I think I should note is that I enabled "ultrafast boot" via my UEFI before this, which even said that it boots so fast that I won't be able to access the UEFI without the OS. I am about 90% aure that this is why I can't access my BIOS and why none of my deices are loading. Yes. I know how stupid I look right now, but that's what I did. Disconnecting and reconnecting my devices does nothing, so I'm stuck with a computer I can't fix through 'normal' means.

That's just about all the context I can think to add. For the record: I am well aware that these forums probably aren't the best to get help on this, and that this may not be the best category for it, but due to my distaste for Reddit and, as far as I can tell, a lack of any resources on this sort of thing from Xanmod themselves, these forums are probably my best bet. And I'd rather get chastised for posting to the wrong place than attempt to fix this problem myself and end up making it worse. I just want to get this resolved as soon as possible. Any help on this would be appreciated.

UPDATE: I tried using the keyboard that came with my computer, and somehow that worked. It must be that Ultrafast Boot is set to load that keyboard's device driver, but not any other devices that didn't come with the computer. Using that keyboard, I was able to go to my computer's UEFI and disable ultrafast boot, and even get Xanmod working by disabling secure boot, but it had issues using my Nvidia graphics card, even with the proper drivers installed, and I wasn't in the mood to spend even more time debugging things, so I just ended up reverting back to the newest 'stock' kernels. Tl;dr: Ultrafast boot is terrible, don't use it.

[MiZoG]

Hello Crigence and welcome to Mint forums

So... input devices work at grub bootloader screen? If not, I say this looks like a UEFI ("Bios") setting-related issue and not Linux-related.
If you lose input capabilities at the next phase of booting into Linux, then suspecting xanmod kernel as the culprit is reasonable.

You can normally access "UEFI Firmware settings" via Grub bootloader's menu.

From the same menu screen you can select "Advanced Options" and load a previously installed kernel, boot into your system and uninstall xanmod.

Though the problem seems to be about secure boot ("error: bad shim signature"). Cannot be sure. You might have installed xanmod unsuccessfully no less. Try to disable secure boot if you get into your UEFI settings at least temporarily.

Generally speaking, I wouldn't recommend replacing "official" Ubuntu kernels with third-party kernels for most usages and users.

[Crigence]

Hello

To clarify: The issue was that I had ultrafast boot on, and because of it none of my devices would load at startup, even in GNU Grub, so I was stuck at that screen watching it timeout to attempting to launch LM and then attempt and fail to load the Xanmod kernel, which couldn't load since I had secure boot on. I actually solved it today by trying the keyboard that came with the computer, and somehow that worked. I was able to use it to turn off ultrafast boot and eventually get my computer running back on the normal kernel, so all's good on my end

My highly uneducated guess is that ultrafast boot was forcing the computer to skip loading any devices at startup, screwing me over. Not sure what I would've done if I didn't keep that keyboard, but I still hope this thread helps someone else in the same obscure situation as me in the future