Since you're using btrfs, there is likely another subfolder under /mnt. ll /mnt will tell you this, but the drive isn't still mounted from the other day. When you're mounting the EFI partition, you're going to want to mount it to that folder, and not /mnt itself (/mnt/root/boot/efi, instead of /mnt/boot/efi) same for the binds (/dev, /proc, /run, etc)

Could you send me the output of lsblk -no FSTYPE /dev/sda3 and ll /mnt?

Apologies, I think I got a bit ahead of myself in the description.
Once you've determined which partition is which (in your case, /dev/sda1 does appear to be the EFI partition, and /dev/sda3 appears to be your root partition), you need to mount them in this order

mount /dev/sda3 /mnt
mount /dev/sda1 /mnt/boot/efi

That's alright, I'll do my best to walk you through it.

Your drive contains multiple partitions (/dev/sda1 through /dev/sda3).
One of these drives is going to be your EFI partition. This is what your system can read before linux boots, your BIOS can't understand ext4 / btrfs / etc, but it can understand fat32.
If you run lsblk -no FSTYPE /dev/sda1 it should return vfat if that's your EFI partition. That's what we're going to mount to /mnt/boot/efi

I'm assuming that /dev/sda3 is your data partition, e.g. where your linux install is. You can find the filesystem format the same way as your EFI partition. Edit: After determining which partition is which, you're going to want to mount the root partition, and then the EFI partition
mount /dev/sda3 /mnt
mount /dev/sda1 /mnt/boot/efi

Unix systems have theology of "everything is a file", all devices and system interfaces are mounted as files. As such, to be able to properly chroot into an offline install, we need to make binds from our running system to the offline system. That's what's achieved by running for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
This is just a simple loop that mounts /dev, /dev/pts, /proc, /sys, and /run to your offline install. You're going to want to either add /sys/firmware/efi/efivars to that list, or mount it (with -B, which is shorthand for --bind, not a normal mount).

Once you've done this, you should be able to successfully chroot into /mnt (or /mnt/root if running btrfs)
At this point, you should be able to run your grub repair commands.

What model?

Nah the demands aren't crazy, they all used to be standard until the mass enshitification hit. My sister's boyfriend found one that had almost all of those bar from the hole punch and the trustworthy manufacturer (some off brand Chinese company I don't remember off the top of my head). Even had a thermal camera on it which was cool

What kind of stuff are you looking for?

Huh didn't realize that would've come with 32 bit so recently. I ran a z2 force up until about 2 years ago when it stopped holding a charge. Those old Motorolas were great phones, but I haven't found anything in their recent line that interested me. Ended up going with a Pixel 6 and then a 7 pro, my dad needed an update from his z2 force and it was cheaper if I just gave him mine and upgraded. Haven't had any issues with the pixels, except for my sister dropping her 2xl and breaking the screen. Anything you get eventually though get unlocked. Tensor has a bunch of custom roms now so anything you upgrade will last for a while.

I hope that charging for basic stuff never comes. I doubt it since like the first thing MSFT did after buying it was to make some pro stuff free (like private repos)

Yikes that's steep! Hard to warrant that over carrying a capture card and a keyboard. Thank you for the link though

Devastated over two button nav being killed off. I love having a back button but I like the swipe to switch apps and to go home.

I have a magisk mod that puts it back in but it's now extremely broken thanks to Google and it doesn't seem to work on new installs. Stopped working properly around May '23 update. P7 Pro

I had a Kodak printer. The first reload I put in it was off brand and it proceeded to immediately brick itself. Refused to recognize any cartridges even the originals.

Also EcoTank is Epson, super duper recommend. I use to sell printers and I would only sell Brother and Epson.

If you've got any questions about them I still have my Epson contact in my phone