If the company I work for mandated a full-week return to the office, I would leave without any shred of doubt. I know that I can get something better, somewhere else, where they will let me work in a way I'm comfortable to work. Employers are opening their eyes to this more as time goes on too, lots of job ads in my sector emphasise that they use true hybrid working but I realise this isn't something that's possible in every sector.
2/3 days a week is fine, but I have no intention of commuting and losing 2-3 hours every day, where I'm not paid and I'm relatively miserable. The question employers need to ask themselves is what perceivable, tangible benefit does office attendance actually bring to their people? Beyond the social aspect, I don't see one. That's their problem, it certainly isn't mine.