Officially, Paramount considers all on-screen Trek (except the Kelvin movies) to be the Prime timeline. But here's a breakdown of all of the timelines:
The "original" timeline was seen on TV and movies from 1967-2005, and includes ENT (2151-2155), TOS (2266-2270), TAS (2270-2271), TOS movies (2772-2293), and TNG-VOY (2364-2379). All novels published up to 1996 take place in the Prime universe, and also the newer ones since 2021 set during each series are also in the Prime universe.
The TNG/DS9/VOY relaunch novels, and their subsequent spin-off series were originally meant to take place in the Prime universe too, but after the new Paramount+ shows started in the same part of the timeline, they were retroactively moved to an alternate timeline that branched off starting with the Enterprise's return from the past in First Contact. This timeline continued through the Coda trilogy in 2021 (set in 2387). That timeline is now effectively ended, but I really like the send off it got and it feels complete.
Another timeline branch occurred with 2009's reboot movie, where Nero and Spock travel from the Prime timeline in 2380 back to 2233, creating the Kelvin timeline seen in Star Trek (2009), Into Darkness, and Beyond.
The new Paramount+ shows are meant to continue the Prime timeline, and I think it's fair to say that all of the 24th Century shows do. Lower Decks is set in 2380 just after Romulus is destroyed and Nero and Spock travel back in time, Prodigy is set a few years later in 2383, and Picard is set quite a bit after that in 2399. I also have problems reconciling what we've seen in Discovery and Strange New Worlds with the Prime timeline as seen in TOS. I fully understand the cosmetic updates for practical purposes, but there does seems to be some other retconning going on that rubs me the wrong way (even if I do enjoy the shows). Luckily for us, SNW's recent episode "Tomorrow and Tomorrow and Tomorrow" gives us a hand-wave explanation for those deviations: Somethig something Time War whatever. This is convenient for the writers, as it clears away canon discrepancies, but also as a viewer I appreciate them giving me a reason to consider these new shows to be an alternate branch of the timeline, apparently from somewhere back pre-1990.
The original timeline of TOS and TNG-VOY will always be my favorite, and I also prefer the novel universe to the new 24th Century shows, so for me, that remains my personal "Prime" universe. The Kelvin universe was a fun side story to follow for a bit, but I tired of it quickly and I'm kind of glad we've abandoned it. I do enjoy the new shows, but for my headcanon they are all now solidly in a Beta universe that runs closely parallel to my "Prime".[/I]