This is similar to the unsolved, closed question here: Quarto crashing with GitHub
I was able to commit and push to Github with only a single presentation in the main Project directory. When I put a single presentation in a subdirectory, it caused the Git tab to freeze.
I removed the offending directory and was able to commit and push a subdirectory with two large PDF files with no problems.
I put the offending directory (with a very simple Quarto presentation) in a different R Studio Project and it caused the same issue.
Does Quarto just not know how to play with Github? Seems like a bug, not a feature.