I was upgrading to 20.04 from 19.10 and the install process froze (probably b/c I was being an idiot and running other applications at the same time). So after rebooting my computer is basically corrupted and won't boot. I was planning to reinstall ubuntu from an ISO image on a USB stick. Is there any way I can recover files from my user $HOME dir on the harddrive?
0) Always make a backup and verify the backup before performing surgery on your OS.
1) Use the LiveUSB you were going to use to reinstall with. Boot into its Ubuntu. Look in the filesystem for the internal drive and its /home to see how big /home is. If you have room on another USB flash drive, copy its contents over to the other flash drive, for a selective copy back once you've installed the new OS.
2) Don't have room? Using gparted, shrink the partition with /home on it and commit the change with the green checkmark in gparted. Move it to the end of the drive, and commit that change with the green checkmark . Then install the new OS into the space you made with the shrink-and-move.