There are also rumors that Mania 2 is in development at Christian Whitehead's new studio, though we don't know if it will also be ready by 2021. But it definitely seems like we will get at least 1 big Sonic game in 2021 for Sonic's 30th anniversary, possibly 2.
I sure hope so.
Sonic Mania was the best thing since Sonic 2 and well the best thing apart only Sonic 2 as well.
It was extremely well received critically and in the fanbase, so not making more of it would be really stupid.
I wish they would make an even bigger game this time, with like 6 new zones plus 12 remakes. They can even throw Sonic Mania owners and add-on to play those zones in that game too.
A man can dream...