I work for an international company and most of us are now officially hybrid workers. In practice, in my department, most of us were already. Few of us were in every day of the week. In EMEA, we've been working like that for the best part of two decades anyway, so there's been a lot of eye-rolling about the return to office training which points out you might now have colleagues in different locations, even different timezones (though if this means people in the USA remember not everyone works there, so a meeting at 5pm EST won't get much attendance from those of us on this side of the Atlantic, it will be a good thing.) The people I'm working closest with at the moment are in Ireland and the Netherlands, so being back in the office makes no difference to how we work.
Some roles do have to remain in the office. Certain contracts can only be worked on by staff in a particular country. There are some restrictions about taking kit (laptops, phones) to certain countries, though most we have offices in are okay. Some workers were already on homeworking contracts - others are moving to homeworking contracts. We already had some people living a few hundred miles away and coming in just once or twice a week, which was their choice.
In the past, some people have moved countries, but if it's for more than the odd week here or there, you will get asked to change your contract. Different countries across Europe have very different rights when it comes to things like redundancy and pensions and health care, so however much you like the location, it's worth checking if it's really going to work in your favour.
For the rest of us, it's very much dependent on their team. Some have been told they must be in the office first Tuesday of the month. (HR are apparently getting a bit twitchy about the chance of there being too many in on one day, as we're not at full capacity in the office currently, with useable desks being separated.) Some are every Wednesday. Some have been told, don't come in for work alone, only if you have sociable reasons too.
My manager doesn't really care, as long as he can contact us, wherever we are. Our team is already spread three different UK offices, Netherlands, Belgium, Germany and Ireland, so online meetings are normal. I think he's going to try and sort out one day a month where most of us can be in to go to lunch together, but I don't think he'll be insisting on any particular day otherwise. I suspect that once the schools are back, some of us will settle in to one or two days back in on days that others will be around. Certainly most of us agree that if you're going to be sat in the office on your own, you might as well be sat at home on your own (unless you have technical issues like Internet problems, or really need a break from the family.)