I wanted to add django but their issues aren't on github as they are using their own system. IMO an external issue tracker lead to a higher barrier to create new issues, so this isn't not necessary fair.
Also fastapi allows people to ask questions with the issues. On the 1000+ open issues, 826 are tagged as question.
It's hard to find a fair metric. Open/close ratio rewards older project with fluctuating/stable popularity. Fastapi popularity is still growing[0], so having some difficulties to work on issues is expected.
django, 1101 open, 32662 closed
cherrypy, 218 open, 1505 closed
starlette, 31 open, 570 closed
pyramid, 70 open, 966 closed
falcon, 168 open, 789 closed
flask, 14 open, 2318 closed
fastapi, 1044 open, 1855 closed
Fast api has one of the worst ratio regarding open/closed issues.