First of all, congratulations to the poster's parents. They have been together for 20 years. It's not easy. I really like it.
If you want to give a gift for a wedding anniversary, of course it should be festive and warm. I think the poster can give his parents a wedding doll. Now it can be customized online. Just provide wedding photos. There were no wedding photos in the era of his parents. The poster can use their wedding photos at that time. This kind of doll can adjust the atmosphere and is very memorable. Last time, my friend customized a couple doll in Tang suits for her parents, and her parents liked it very much.
Or the poster can take his parents to a photo studio to take a set of photos, let his mother wear a beautiful wedding dress, and let his father wear a handsome suit, so that they can return to their youth and be sweet again. Haha.