I know the resource pack says 1.21.3+, but theres no version for 1.21.5. I'm lowkey scared because I've used a 1.21.2 version of Fresh animations on 1.21.3 and it nearly completely broke.

Just try running it on 1.21.5
It's easier and faster than asking

True I guess, It did work fine so maybe you guys should make the resource pack say it can work on 1.21.5 on modrinth