I can't see anything graphics-related happening or going wrong.
This sounds like a lightdm problem. Maybe this is it:
Mar 28 10:16:56 testvm lightdm[934]: pam_succeed_if(lightdm:auth):
requirement "user ingroup nopasswdlogin" not met by user "test"
** Package changed: xorg-server (Ubuntu) => lightdm (Ubuntu)
** Changed in: lightdm (Ubuntu)
Status: Incomplete => New
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https://bugs.launchpad.net/bugs/1868780
Title:
[virtio] Xubuntu 20.04 - Blank screen after login
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