I have 2 nieces who are true adults. I still send Christmas cards/birthday cards, but gifts stopped once they were "adults". For Oldest niece, that was when she graduated college (also when she dropped off the "kids gift exchange" for the family). Although during her college years, it was more "send her a gift card for a local to her restaurant during exam week" which I later found out was actually used as "I'm starving and need food" when she was in grad school and her parents had cut her off from money from them. Her younger sister was pregnant the summer after she should have finished high school, so I switched to sending gifts to her daughter instead of her at that point. (I still sent the normal graduation presents when she finished her GED a couple of years later.)
Now I've got two nieces in college and a nephew just starting, but I haven't been as good about sending stuff during exam week, etc. (Plus, with COVID, they've been at their parents' houses most of their exam weeks.) So, I'm back to money in their birthday cards and getting them a gift at Christmas. But once they graduate and become "real adults", I'll drop back to just cards for those, too.
-Kris
DS (9/05)
DD (8/08)
DD (9/12)