Star Trek: Enterprise in the Kelvin Timeline
It's canonically established that Star Trek: Enterprise is set within the Prime Universe rather than the Kelvin Timeline, but the show technically belongs in both.
The Kelvin Timeline debuted in the 2009 Star Trek reboot movie, directed by J.J. Abrams and starring Chris Pine as James T. Kirk. This movie replaced the original cast with new actors, but its biggest twist revealed that it wasn't a traditional reboot.
Instead, every other Star Trek TV show and movie that preceded it remained part of the main canon, only in another timeline.
The return of Leonard Nimoy as Spock Prime alongside Zachary Quinto's new version of the legendary Vulcan confirmed this.
The show's main canon status is still debated among fans, with some arguing it belongs to the Prime Universe and others claiming it could be part of the Kelvin Timeline.
Author's summary: Star Trek Enterprise may belong to both timelines.