The 13.18.4 feature illegal_namechar_replace doesn't support replacing * (for example) with 🞰 as it automatically replaces it with � when used. Pasting 🞰 manually into a filename works, so the issue appears to be with the feature itself.
It looks like the issue is that it's not in the Unicode Basic Multilingual Plane (BMP) unlike some other Unicode characters which work. Supplementary plane Unicode characters (those with surrogate pairs, which 🞰 has) likely all don't work (untested).
There should probably at least be a check on trying to set illegal_namechar_replace to unsupported characters, because being able to do so and it not working gives the impression something is broken, especially in the context of 🞰 being supported when pasted using inline rename etc. Ideally there'd be no misalignment and it'd just work.
Thank you for the fix, it works. However another similar issue has come up:
I'd like to replace forward slash / with an alternative, e.g. / (Fullwidth Solidus), but despite defining a pair via illegal_namechar_replace, a new directory is always created (slash is inserted instead of the replacement character). I was hoping this feature would override the create-sub-folder functionality (since both slashes work, I can use backslash for that instead if I leave it not replaced). Would be nice if this made it into the next release. DO v13.19.