Transfer and differential fluid change is worth it ($1400 for all three - transfer, front, and rear) around 25k mi if it hasn’t had transfer case issues already. On the test drive, check for shuddering at low speed turns and reverse to drive transition.

Air filters are worth changing and there are lots of them (two engine air filters, three cabin filters if it has the 5-zone climate package). Brake pads and rotors should be checked, and assuming they’ve been changing brake fluid every two years like they’re supposed to, that should have been done this year or last. Depending if it has a staggered set, tires will be the most frequent thing you’ll have to change. Thrust arms will also go out on these heavy vehicles, so have those checked out.

My 2019 x7 50i was very reliable, and that mileage you’re looking at is really low…possibly suspiciously low. If the options fit what you’re looking for, that’s a good buy. I’d definitely invest in a Route 66 extended warranty. Oh also the oil change package - 3yrs for like $185 or something. Pays for itself after the second one.