Hi, My Gnome 3.34 on debian unstable started acting the same after gdm3 got upgraded gdm3:amd64 (3.34.0-2, 3.34.1-1).
What I was doing before this was to try bumblebee to handle having both intel and nvidia graphics card in this laptop. And then removing bumblebee. Then doing a upgrade installed new version of gdm3. And now I can not get the desktop up and running. And I have no idea how to troubleshoot this. gnome is now up at 3.34.1, mostly. Jens Yllman