2021 core games will be Pokemon Glimmering Pearl and Pokemon Corrupted Diamond. Some hints, like the Calyrex battle theme being similar to the DP trainer batte theme and the Regigigas secret event, were in the Crown Tundra.

The cover legens aren't, as many believe, G-Max Palkia and Dialga (even if there are new forms for them), but an ethereal-like form of Arceus and Voideity(Dark/Dragon) ,a new legendary (linked to Eternatus).

In the games, Team Galactic doesn't exist and you will encounter a creepier menace during your adventure. The rival and the professor are still Barry and Rowan.

Some mons of gen 5-8 are now present in Sinnoh, and some of them has a regional form. This forms are still in the making but I am certain that Skiddo has the fire type and has a sinnohan evo called Moltex that resembles a bulky ibex with boiling horns that is fire/ice type.

As many predicted, the Mt Coronet will be converted in a wild area. From what i know they could make another smaller wild area near Stark mountain.

Gigantamax for:
Starters
Luxray
Garchomp
Hypno
Gliscor
Honchkrow
Mismagius
(there are other forms still in progress)

On November 26th (cake day) a teaser image will be posted in the pokemon website from nowhere, portraying an enormous poffin with dynamax clouds above it.