I'm not sure, I haven't used the mono version. I know for the non-mono version it's just downloading it and running (to the best of my knowledge).
Have you tried making a new project and running that? Also, maybe download Godot again and see if that fixes it?
Other than updating your drivers/computer, I'm not really sure. I have very little experience with the mono version of Godot. Sorry!
(Also, you don't need to mark a response as an answer unless it's answered your question/problem/thing. I'm assuming based on your post, the question/problem/thing has not been answered yet, if it has, then disregard this message :smile: )