VNC with XFCE freezes on Ubuntu 20.04
Solution 1:
I uninstalled tightvncserver:
sudo aptitude remove tightvncserver
and installed tigervnc:
sudo aptitude install tigervnc
In my case I had to edit /etc/vnc.conf since the defaults didn't work for me, but YMMV.
After 10 minutes, no freezing, and the xfce4 windows are now drawn properly with their window borders and controls.