How to turn off wifi so that it doesn't turn on unless I want it to

I see a lot of this type of question and the answers are always "turn it off in settings". Yes, this used to work for me, but now it doesn't, maybe after an update. It turns on again overnight.

Also, it seems to turn on when it is in range of a wifi I've been to before (or even a chain business like an airline or hotel. This is VERY annoying because many of those chain business wifi sources need a new password or (like airlines) are only local to the plane. The phone will then not have cellular internet OR wifi internet.

I repeat: I DO turn if off in the settings and it is still turning back on by itself.