A lot of my irl friendships started out as online friendships, so I'm sure if it counts, but I draw them their OCs for their birthdays c: Some examples:
As for friends that I've known only irl since the beginning- I used to make birthday cards for my coworkers from my team in my previous job. It was actually a collab, other girls from the team would throw ideas, I drew it, someone else coloured it, and we all signed it. It was nice
I also do Christmas cards myself! And with my friend from highschool we had a tradition of drawing birthday, christmas and sometimes easter cards with small drawings of us (the drawing is ugly but at least I see the progress in my art journey haha)
For my other friend's birthday I made a whole comic. I don't even remember what was it about but I kinda hope she doesn't have it anymore, as I was 14 back then and I don't relate anymore to by sense of humour from those times cx