Got it!!!
I moved to X11.
sudo vi /etc/gdm3/custom.conf
I commented out the line
WaylandEnable=false
restart the system.
All issues have been resolved!
Conclusion: ImageView does not properly support Wayland.
For the parsing warning, I had to revert back to Adwaita theme.
Given that X11 seems to be on its way out, maybe it should be looked at.
@danielwe should I create an issue at ImageView Github repo? Is that the way to do?