Were not getting Horizon 5 next year. Probably motorsport. We were actually supposed to see Motorsport gameplay at E3 and iirc the Forza team said look forward to playing it later this year on stream. I assume covid and some people from the forza team pitching in with Infinite delayed the game to next year.
I'm not so certain on Motorsport reboot in 2021 personally. According to an interview, it only began full development in December 2019, before that they were mainly working on the new ForzaTech engine and working on DLC for Motorsport 7 and Horizon 4. A November 2021 release would give it less than 2 years of full development, and since they're starting over from scratch with all new tracks and all new car models instead of reusing tracks and cars from Motorsport 5-7, they'll need extra dev time to get enough cars and tracks ready to satisfy people, they don't want to run into a Motorsport 5 situation again with critics attacking the game for not having enough cars and tracks on release.
In theory at least, Horizon 5 should have been in development longer, assuming they put it into full production as soon as Horizon 4 released, September 2018. So Playground could get a cross-gen Horizon 5 running on the old build of ForzaTech out in 2021, but if they decided to wait on Turn 10 to finish the new build of ForzaTech, and engine that wasn't ready until late 2019, we might not see any Forza game in 2021 sadly.