Here's my Sonic Sona Chelsea the Cat in a Classic Sonic style.
I stated that the Classic Era takes place 4 years before the Modern Era.
Sonic Generations said the Classic Era is the past. Archie Sonic Post-SGW said so too.
Sonic Mania and Sonic Forces however says the Classic Era is another dimension. So think of the Classic Era in Sonic Mania and Sonic Forces as the Miniverse like Skylanders has.