Sonic Mania's sequel was never developed due to Sega's concerns

Sonic Superstars is regarded as Mania's spiritual successor.

Sega really confuses me at times : r/SonicTheHedgehog

Sonic Mania: Most Up-to-Date Encyclopedia, News & Reviews

Sonic Mania Plus - PlayStation 4 : Sega of America Inc: Video Games

Sega Rep Says the Company Is (Usually) Fine With Fan Games—As Long as They Aren't Monetized

Christian Whitehead Is On Good Terms With Sega, And They Never Planned To Make Sonic Mania 2 - Gameranx

SEGA and Sonic Mania developers explain the lack of Sonic Mania 2 - My Nintendo News

Sonic Mania, Awesome Games Wiki

Sonic Mania Developer Very Unhappy About Origins!

Sonic Mania Plus Announced - Siliconera

GameInformer: Why Didn't Sonic Mania 2 Happen? : r/Games

No, Sonic Mania 2 Wasn't Cancelled Because of Bad Blood Between SEGA and Evening Star - Games - Sonic Stadium

Sonic Mania Flourishes Native Problems as Prolific Solutions - digitalchumps

Sonic Mania Dev Confirms Superstars Translates 'Retro Engine' Physics Into 3D

Sonic Mania review

Sonic Mania review