As I’ve stated in my previous message:
This issue is not caused by the lack of GPU because I’ve tested this program it non-Qubes virtual machine without GPU as well but it works fine there.
So this is a Qubes OS bug with GUI and it needs to be fixed by Qubes OS developers.
But for them to look into this problem and try to fix it you need to report this issue to them in the Qubes OS issue tracker to make them aware of this problem:
Issues · QubesOS/qubes-issues · GitHub
Issue tracking | Qubes OS