My VM was configured to VBoxSVGA in 6.0.x with dual screen (I was unable to have 2 monitors with VMSVGA) with 3D Enabled. All was working correctly (little slow, I doubt the 3D mode was really working)
- After upgrading to 6.1 at the firstboot in VBoxSVGA with 3D mode all work correctly.
- I've switched to VMSVGA, Xorg is unable to start "failed to create screen resources(EE)"
- I've switch back to VBoxSVGA, now in the GUI I can't enable 3D mode on it.
- I've start the VM, Seamless mode is no more working (not resizing)
- I've edit the VM setting via VBoxManage, to enable 3D mode. Not better
- I disable 3D mode again, only one monitor
- I've switch back to VMSVGA with 3D Mode, Xorg is now working but only on one monitor
Host: Windows 10 build 18362 x86_64
Guest: Ubuntu 19.10 / 5.3.0-24-generic #26-Ubuntu SMP Thu Nov 14 01:33:18 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
*EDIT*
* So now I've switched back to VBoxSVGA with 3D mode enable and 256MB via vboxmanage. Dual screen is working, the auto-resize is still broken but with a screenlayout profile it does the job.