Not sure why so many things use the compatibility form of normalisation.

Some older RFCs even recommended using it for passwords, which needlessly reduces entropy (yes we need to normalise passwords because of combining characters, but we don’t need to collapse symbols that a user can choose from, like ſ and s).

In my opinion, the compatibility form makes mostly sense for searching text, and even then it’s sometimes annoying (I want to search exactly for ss and not ß, browser). If you know of other good use cases let me know.

It also OK to disallow registering two identifiers with the same compatibility normalisation form (edit: this does not prevent all homoglyph attacks BTW, that is another can of worms), but I don’t see the need to normalise the identifier when it’s used.