PS5 Player using "Generic Player"

As far as I know, you can still build custom profiles. This is the most definitive post I can find on the topic in general though:

Modern Plex client apps rely on the hardware they’re running on to report their capabilities accurately. If they don’t, then there can be problems.

I suspect there may be edge cases where the Plex app can’t accurately find a device’s capabilities and traditional profiles may be necessary.