Logging out took a few dozens of seconds. The journalctl output shows
issues with nouveau and Xorg at that time:

Jul 20 17:39:39 qaa kernel: nouveau 0000:01:00.0: Xorg[1491]: failed to idle channel 4 [Xorg[1491]]
Jul 20 17:39:40 qaa kernel: audit: type=1400 audit(1784561980.053:3137): apparmor="ALLOWED" operation="open" class="file" profile="Xorg" name="/etc/glvnd/egl_vendor.d/" pid=1042547 comm="Xorg" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
Jul 20 17:39:50 qaa kernel: nouveau 0000:01:00.0: Xorg[1042547]: job timeout, channel 4 killed!

and

Jul 20 17:40:02 qaa kernel: nouveau 0000:01:00.0: gsp: rc engn:00000001 chid:4 gfid:0 level:2 type:109 scope:1 part:233 fault_addr:0000000000000000 fault_type:00000000
Jul 20 17:40:02 qaa kernel: nouveau 0000:01:00.0: fifo:c00000:0004:0004:[Xorg[1042547]] errored - disabling channel