I also noticed fewer AUs. I can enjoy them meeting as adults, but I agree that it changes the dynamic. Most AUs I've seen that keep that are the kind that keep the origin story plot more or less but twist the universe or the character with a trope, like genderswap AUs, making one or both a werewolf, BSDM an A/B/O universes, or adding daemons.

I'd like to see more canon divergence AUs. There are some though, like I've read AUs that have Bucky escaping Hydra before Steve is found, or ones were the serum worked differently or such.