Oh gods - I've never worked at a place with unlimited PTO and that sounds miserable. I'm a highly visible employee who fields a lot of questions from junior and intermediate folks - taking a three week block off always means the other very senior dev needs to shoulder the load (but we're on good terms and happy to see each other balance work and life)... more senior folks would be less able to take vacation due to how much more visible their absence would be.
It should be ok for absences to be visible. And if they are more than just visible, you have a bus factor problem, and past a certain company size that's not something you should have.
But if it's a question of balancing your standing then it's all about visibility. If I'm off in a corner working maintaining some legacy system as a team of one that has somehow failed to be replaced in twenty years then I could just continuously be on vacation - additionally voluntarily taking odd working hours (like working 8PM-4AM) would also make it much less obvious that you're snogging vacation... except to the management team which usually can't comment on things like that except to consider firing you.
I haven't done it for a while but I've certainly taken off 3 weeks at a time previously. And if you count a combination of work travel and PTO, I did it last about a month before the pandemic hit.
And as others have noted, taking multiple weeks off is quite normal in Europe.
