We have not gotten any information if they will make DLC for the sims4 in 2021, but I assume that they will. The surveys are hinting for maybe one more year of packs.
Now as for when they will announce the sims5, I don't think it sounds unlikely that they might announce that they are working on it next year because next-gen consoles are released by the end of this year and EA would probably want their studios to show what they are working on and I really hope that EA/Maxis will not do what Rockstar are doing and re-releasing their old game for the next-gen consoles... Sims4 for the PS5, no thanks.
But depending on where we will be with the pandemic we might not get an announcement until 2022.