Filevault stuck on pause, can't reinstall macOS, can't upgrade
So I figured I've tried all I can so let's just try erasing the disk. That worked.

Here's what I did:


Time Machine backup to a disk.
Time Machine backup to another disk because I'm not risking it.
Recovery mode.
Disk Utility -> Select Macintosh HD -> Erase.
In recovery mode, Recover from a TM backup.


Now the system's good!