> we are combining those urls to create a unique sharing link.

Just hash them into something shorter? You can calculate the risk of collisions based on the expected volume of files/users, or since you control all the hashes anyway, you can just do a quick lookup to make sure that particular hash doesn't exist already? If you want to do something more human-readable, you can also consider "gyfcat" style URLs or look up "adjective adjective animal" hashers like https://cli.r-lib.org/reference/hash_animal.html

Or use a UUID?