Solution: There never was a second drive. It must have been a partition that got wiped with the install, but there's only the NVME in there. Sorry, guys. I dig around in my innards very frequently and just thought I was mounting a second drive this entire time. Hooray for backups.
reinstalled Mint and my second drive is absolutely invisible to everything. I can't mount what I can't see. I'm thinking of unplugging it and plugging it back in just because I'm out of ideas.
What could have caused a drive to become invisible after a reinstall?
Edit: Checked bios. All security disabled. Using AHCI and UEFI (tried CSM). I don't really know what these things mean, I just know things were working properly before I reinstalled mint so I'm puzzled why it could be a BIOS issue.
Current lsblk: