https://www.nexusmods.com/pokemonbdsp/mods/1?tab=images

This ROM Hack is a full conversion of Brilliant Diamond 1.3.0 to Platinum. It has 493 Pokémon at the moment including Sylveon and Regional Forms.

It can be played on a modded Switch or RyujiNX.

Documentation for the hack : https://luminescent.team

I’m not affiliated with the team but I’ve been active on their discord server and they announced 2.0F will be the last update for the hack, baring bug fixes.