As for me, it's always no longer be the Sonic series I grew up with after 1999.
I grew up with Mega Drive Sonic, Archie Sonic, and DIC Sonic.
Dreamcast Sonic and what's happened after that was when I already in college.
I don't mind any change to Sonic since they've got to attract new fans anyway.
They can't always rely just to old Sonic fans.
As long as the change is just meant to attract Gen Z-A, not just because of DEI pressure or just to please some loud and vocal influencers on Twitter.
Both of my sons are Gen Z-A and while they still love playing Mega Drive Sonic games they don't like Archie Sonic and DIC Sonic.
They aren't from my generations so I understand that.
The change from Classic-era ot Dreamcast-era of Sonic lore I accepted because these changes had little impact on the lore.
So what it's no longer set on Mobius, that just means it's set on Earth all along and the characters are relatively the same.
What I'm against is Amy Rose personality being tweaked to the point she is out of character.
I'm against characters simply coming back to life for marketable appeal.