This is all based on a full capacity:
I sit in the Gwladys Street, which has a capacity of 10,611. There are from recollection seventeen turnstiles, so that's 624 people passing through each 3ft space.
You then have this number of people leaving through a small number of larger exit gates post-match, with arguably a smaller period of time to allow movement.
A Boeing 737 Max, newest of small planes, has a maximum seating of 200ish, which is at maximum capacity based on reduced legroom at full capacity.
Then you have congestion points including toilets, stairs and refreshments, and that's before considering contamination of said areas through physical contact.
Planning wise, it won't happen. That's before considering how thousands of people have died and will continue to die without having stadiums open, so...