BDSP will have a dlc in March 2022. A new area will come with this which is a little island to the right called the enchanted island. This is a small island all about fairy type Pokemon (other types on island too). There will be 1 new fairy Pokemon called spellostic. This Pokemon has a pointy head, feminine looking on 2 legs and wings with the body being majority green. Rumour has is that Spellostic uses magic to make the island disappear but a scientist has you team up with him and follow his lead which eventually gets you to the enchanted island.
Along with Spellostic, another 62 pokemon not in BDSP will be on this island.
In BDSP you will find new fossils in the grand underground such as the sliced fossil. In the enchanted island, you can revive these new fossils and they become the new Pokemon that are in the legends game such as Hisuian Growlithe, basculegion etc.
the DLC will be cheaper than SWSH dlc by roughly 39%.