at the log in screen, there is a small gear wheel on the bottom right side, choose “Pop on Wayland" (edit: if you want COSMIC DE to work too, see update below) (edit2: if you can't see the gear wheel, see update2 below)
.
update:
there are some settings on the virt-manager to make COSMIC DE works.
if you don't need to run COSMIC DE, can ignore the following
Display Spice : Type = Spice server, Listen type = none, uncheck password / opengl
Video : use QXL (instead of default Virtio)
new step 8. at the log in screen, there is a small gear wheel on the bottom right side, choose “COSMIC"
.
update2:
sudo nano /usr/lib/udev/rules.d/61-gdm.rules
Goto the line that reads LABEL="gdm_prefer_xorg"
.. commend out the next line .. #RUN+="/usr/libexec/gdm-runtime-config set daemon PreferredDisplayServer xorg"
Goto the the line that reads LABEL="gdm_disable_wayland"
.. commend out the next line .. #RUN+="/usr/libexec/gdm-runtime-config set daemon WaylandEnable false"