Making a list for my sanity (the descriptions get more unhinged the longer i type send help):
Sonic 1 and 2: Happens normally! No timeline divergence (aside from Sonic 2 happening before CD)
Sonic CD: Sonic tries to collect the Time Stones to stop Eggman and save Little Planet, but is caught and roboticized into Metal Sonic. After Eggman is sure that Mobius is throughly in his control, Metal is sent after another timeline’s Sonic [Indigo/Modern], while Sonic’s friends are forced to fight off Eggman’s forces alone. This ends with Eggman being defeated by the Resistance, and the planet beginning to heal as the Resistance try to find leads on where Sonic is now that Eggman’s gone (for now)
Sonic 3: Happens mostly as normal, Eggman tricking Knuckles, going after the Chaos Emeralds, ect. The Angel Island Mural is of a Red Wolf instead of a Blue Hedgehog. Gadget goes Super for the first time, but isn’t able to as naturally harness the Emeralds’ Chaos, and passes out unconscious soon after stopping Eggman.
Sonic Mania: Does not happen in this timeline.
Sonic Superstars: Does not happen in this timeline.
Sonic Adventure 1: Gadget goes Super, Chaos gets sealed away, the world is saved.
Sonic Adventure 2: Shadow was based of Gadget instead of Sonic in the timeline. Plot carries out mostly as normal, Shadow fighting for Maria’s legacy, Gadget fighting for Sonic’s.
Sonic Advanced Trilogy and Battle: they sure happen (do not know their plots outside of Emerl existing and Cream was in Advanced.)
Sonic Heroes: Does not happen in this timeline.
Sonic Rush (+ Rush Adventure): Happens, Blaze is Very Confused (it’s fine Gadget is too)
Shadow the Hedgehog: Ehhh?? Happens but thanks to Heroes not happening it’s probably different.
Sonic 06: Plot proceeds as normal, however everyone remembers the events after defeating Solaris.
Sonic and the Secret Rings: Happens as normal.
Sonic and the Black Knight: Gadget is seen as an evil spirit due to being a Wolf Mobian, Lancelot can sympathize with him. The plot happens mostly the same, Gadget is not dubbed King Arthur, but is still known as the Knight of the Wind. Silver and Jet are also here, due to time travel.
Sonic Unleashed: Gadget finally masters Super form, but then immediately is turned into a werewolf. Plot happens as normal.
Sonic Colors: Happens as mostly as normal, instead of Yaker, Gadget befriends a burst wisp known as Nova. Nova stays with Gadget as a companion, and Tails starts researching Hyper-Go-On energy afterwards.
Sonic Generations: Does not happen in this timeline, no Sonics to Yoink
Sonic Lost World: uuggghh fine.
Sonic Forces: Plot carries out mostly as normal. Gadget, being the Modern equivalent, is captured by Eggman, and tormented by Infinite and his illusions. The Resistance believes Gadget was roboticized again due to the illusions from the Phantom Ruby. Classic Sonic does not appear, and the role is filled by Silver the Hedgehog instead.
IDW (Metal Virus): Finally breaking from the pressure of everything, the strain of keeping himself from getting infected, and the fear for his friends, Gadget puts an end to Eggman, permanently. From here on out, Starline and Infinite take over as main antagonists.
Sonic Frontiers: Plot carries out mostly as normal, Gadget begins seeing hallucinations due to the effects of the cyber corruption on him as a previously roboticized mobian, including those of Sonic and Metal, as well as Infinite and his previous self as Metal Gadget. Sage sacrifices herself to save everyone, Gadget and Tails work to rebuild her.
MoStH: Current events, Barry is crushing on Gadget hard.