You just gotta prepare something for their birthday next year. No need for something big, just thoughtful. Add a sincere apology or two and I'm sure they will appreciate it.
I also tend to forget someone's birthday other than my partner and immediate family so I just put them in my calendar. No more accidentally forget about friends' birthday, unless I'm really busy and my ADHD acting up.
Very cool! I hope this is this part of a set 🤩