Update: it worked without any issues after i tried a different USB stick with a different ISO. Which is weird, because I had installed LMDE on several machines with exactly this stick. I guess the ways of our Lord and Saviour are mysterious.
I swapped out the SATA drive on the Dell 5070. There is no NVME drive. Before I had a 256 GB drive. I put in a 1 TB drive and installed Mint on it. The previous drive also had Mint. But I must have somehow messed up the BIOS settings because now the blasted thing won't boot.
The drive shows up on the System Info page of the BIOS:
It also shows up in the Drives page:
But I can't choose it as a boot option:
Clicking on Add Boot Option only brings an error that it can't find any file system. I tried restoring the settings but that didn't help. What can I do?
Make sure it's in AHCI mode and not RAID. It's probably a setting under storage, at least on newer ones it is.
Tried that already. Didn't help.