This is probably the best way I’ve seen the timeline put into place.Within the games, there are many different timelines, and Forces muddied the water in regards to whether timelines and dimensions are different things.
Sonic CD: Introduced the Good Future and Bad Future, two separate timelines. Because of how early CD takes place, All of the branching timelines contain their own split off Good Futures and Bad Futures.
Original Timeline: Sonic 1 - Sonic 06. This can also be referred to as the "Solaris Timeline". The timeline ends with Sonic 06, and is the only timeline to contain it. It's also the only timeline in which Solaris exists under natural circumstances. The death of this timeline created the Modern Timeline.
Modern Timeline: Sonic 1 - Present (Forces at the time of this post). Does not contain 06, but has the Rivals and Rush games in it's place. This timeline also exclusively features Sonic 4. Despite being spinoffs, Secret Rings and Black Knight are also canon to this timeline.
Shadow the Hedgehog: Sonic 1 - Shadow the Hedgehog (2005). It contains a number of effectively non-canon endings that never get expanded on in any of the other games, only the true ending is canon in any other timeline. Each of these other endings could be considered their own little bubble timelines we will probably never see again.
Classic Timeline: The Timeline/Dimension created from Classic Sonic's point of view after Generations. Features all the old canon pre-Adventure Sonic games, and has Mania instead of Sonic 4. It crosses over with the Modern Timeline a second time in Forces.
Silver's Future: An odd sort of alternate future separate entirely from CD's Good and Bad Future's that seems to be able to change based on events in the present. It's unclear if Silver is always aware of the changes.
Blaze's Dimension: The world Blaze and Marine are native to, and the home of the Sol Emeralds. It's vague as to if this world is truly separate from Sonic's world, or if it has some connection to Silver's future.
IDW Sonic: The comic timeline. It's separate and distinct from the Game Timeline, but is identical to the Modern Timeline until after the events of Forces, at which point it splits off in it's own direction. Given the ages of characters unique to the comic, it's likely they exist within the game canon as well, regardless of if they end up showing their faces in the games or not.
Sonic Prime (Netflix): Still not much info to go off of right now, but rumor has it it will crossover many of the various timelines within the existing Sonic multiverse.
That's everything canon I'm aware of right now.
The only thing I kind of disagree with (a very slight disagreement) is CD’s Good Future/Bad Future affecting the timeline. All the changes in time during CD are contained within Little Planet, plus the Good Ending (aka all Good Futures) is canon within the series.