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.
I’ve used Nexus to find mods for Bethesda games, but I didn’t know there were pages for Pokemon games as well. Cool.