Looking up

qt.qpa.xcb: X server does not support XInput 2

I discovered 

https://community.rstudio.com/t/x2go-and-rstudio/29704/5

which linked to 

https://wiki.x2go.org/doku.php/wiki:development:glx-xlib-workaround

but following the directions for Ubuntu, I get:

E: You must put some 'source' URIs in your sources.list

Moreover, the directions are for Ubuntu 14 and we're on 20, so I'm not even sure the directions are up to date if, indeed, the problem with x2go still exists after all this time.