To be honest I think 3 days a week in the office is a perfectly reasonable requirement. It gives enough opportunity for people to get face to face time and to build the relationships they need to build whilst still offering flexibility. Should it be combined with some flexibility for edge cases? Sure, managers will always turn a blind eye when it makes sense. And part of that is you can only have flexibility if the base line is established, if 50% of workers are still refusing to come in, the only way to solve that is a mass "Show up or else". In reality in 6 months you have a quiet word with your boss and probably the flexibility will creep back.

Having said that, the way we got here is less than ideal. Senior management at tech companies made a whole tonne of bad promises and poor decisions during the pandemic and they've taken no ownership of that at all. The only reason this has become so difficult is because Senior management didn't have the intelligence to say "Hey, this pandemic is a once in a lifetime event, we're going to be flexible now but we need you to know this won't last".