I have two situations in which I need to run desktops without any 3D acceleration.
1) I often run Ubuntu and CentOS VMs on a machine who graphic card does not play nicely with VirtualBox's 3D acceleration (bug in the drivers).
2) Accessing remote sessions
This isn't a quick "log in and check something", I could be working at them for hours, and the performance hit from using LLVMpipe really annoys me, so I could really use a Desktop Environment that runs on Modern distros but doesn't require 3D acceleration, but I can't find reliable info easily.
Which currently maintained, mature, DEs don't require 3D acceleration (note, I'm not asking for an opinion on whether they are any good, I just want a list).