Here are the main problems:
Whenever I try to open a folder, it displays for about 1/2 second, then closes. But when I open a program (e.g. Document viewer, Open office...) it can browse to find files and work on/save them.
The file-browsers embedded in programs can also find shortcuts which I have created to folders, but these don't appear on the graphical desktop.
Firefox and Thunderbird work, as do other programs I have installed. But in all programs the buttons for minimizing/maximizing/closing are just blank spots (or a kind of miniture blank terminal screen). The pull down menu for system admin is also improperly populated.
At irregular intervals, moving the cursor around suddenly opens the Activities panel without apparant reason.
I have opened a terminal and tried update, upgrade and various other things the web suggests for repairing problems like corrupted dependancies. I have even tried to deinstall/purge nautilus itself using dpkg in the terminal, but that would probably just kill the console process itself. At the moment I cannot even manage to download a disk image of 20.04 to a usb-stick so that I can reinstall it from scratch.
These problems may be unrelated and some are probably the result of my clumsy attempts to fix things. Any suggestions?