At least for those with actual reservations and treaties they are allowed quite a bit of self governance and such. They can make their own laws, form a government as they wish, tax, regulate, decide who is a member and such.

That has not changed at all.

It sounds strange, and it kind of is, but in reality life on a reservation in most cases is rough, few options to make a living, lots of substance abuse, tribal politics can be pretty petty and nasty. I lived near a reservation for a while and the first thing you think "oh man they have this nation inside a nation they could do a lot of things" but really life is rough there.