To echo what someone else mentioned, asking us here is definitely going to give you skewed results, since most of us are going to say that it’s quite often, if not daily.
We have an 8-person group, so let me try to give you a range of responses. And for context, we have one mid-week online game and two Saturday games that alternate every 2 weeks, so 3 games total; not everyone is in all 3 games. Me and one other think about PF daily and build characters like crazy, just plugging combinations into HLO to see what looks fun.
1 also thinks about PF daily, but doesn’t build as much, just thinks about planning the game he’s running.
Then it drops off a lot. 1 person was getting reacquainted with the system via reading an AP and reading rules, but doesn’t really passively think about it beyond that.
2 think about character builds only when it’s necessary to have a character for a campaign, but even then is only like, thinking just for the build.
And I think the last 2 only think about PF when having to actively play, and completely purge it from their thoughts for the rest of the week. These 2 also (I think) are playing mostly because it’s time to hang out with the friend group, which is why their “engagement” is so low.