I just upgraded from 18.04 to 20.04 and when I click on "files" the window will open and automatically close. I'm using spacefm as a workaround but would like to get the originally installed app working again. Thanks!
P.S. I'm also having the icon problems that I've seen written about elsewhere. Specifically, "settings" and "power off" are just blank circles with no text, and on the windows, the resize and close icons are squares but do have text when the cursor hovers over them. I can live without the icons but it would be nice to have them back. The files window is the important issue at the moment. Thanks!
nautilus
from a terminal emulator and including any error messages in your question