I have a little bit of information on the Sinnoh remakes, some stuff is still up in the air, but they are planned to release globally in late November.

-They will be remakes and thus will have eight gyms that lead to an elite 4, of course, headed by Cynthia
-The main story won't have many changes from the original, having regular grass encounters like in the original gen 4 games with certain locations such as the great marsh, the underground and the friend safari acting like Sword and Shield's wild zone
-Pokemon will be able to follow you, but sadly only in certain areas such as Amenity Square and the Pokemon Mansion, which has been greatly expanded.
-No Galar or Alola form pokemon will appear in these games, however if you hatch eggs in the distortion word they will become their alternate regional variant as far as I am aware.
-The postgame is still a little bit up in the air but there will definitely be a post-game Giratina episode, a lot like the delta episode and finally the arrival of the azure flute event, with some Team Galactic shenanigans surrounding it.
-There will be a day one event mystery gift distribution of a shiny Riolu
-The battle frontier will make its return including all of the past attractions
-The underground will function much as it did in the original gen 4 games with secret bases expanded, not unlike the ORAS games.
-The battle zone is back, with the resort house acting as an area to re-battle gym leaders after you have completed the main story
-The distortion word will be accessible once you have caught Giratina
-There will be no new mega evolutions or gigantamax pokemon, however, I am under the impression that there may be new evolutions for Sinnoh pokemon, possibly chimecho, but I'm not sure
-There was talk of a new archeus form but I haven't seen or heard anything of it since