Most places I've worked, there has been a written or unwritten (and, depending on jurisdiction, maybe statutory) assumption that you can take a week or two off without discussion (other than
which weeks, naturally) but anything above that may need some discussion about project impact and timing.
It typically hasn't been a problem if there is lots of notice, but "I'd like to take 3 weeks off next month" is likely to end up with a bunch of back and forth at best.
My current place has a number of international hires, and has been pretty flexible about allowing large blocks of time to go "home" and visit, some mix of vacation time, unpaid leave, and remote work for 4+ weeks. But these have typically been planned many months in advance.