While I never experienced this problem myself ever, I read about it on multiple game threads on this site. Typically it is related to 4K screen or something graphic related. Below is how to fix it, generally. If it doesn't work, then it must be different issue.
Press Shift + G, which will bring up a configuration screen.
Look at the Renderer tab/section, usually it is set to Auto.
Manually pick a specific Renderer starting from the bottom ( usually the GLES works ).
Quit and restart the game. If the issue persists, repeat with different Renderer until you get the one that works.
If you tried all the Renderers and still doesn't work, must be different issue, and better ask in Ren'Py specific forum/site/reddit/discord/etc.