Picard Season 3 directly references several things from the first 2 seasons, one of them being central to the plot, so if you think they're their own timeline, than so should Season 3.
But that doesn't jive with the SNW/LDS crossover episode. None of the LDS characters notice anything 'wrong' about the past. The events in the past line up with what Tendi said about her ancestor being on the Orion 'science' ship and discovering the time portal.
The events of the crossover are also referenced in LDS Season 4, Mariner outright name drops Pike and we see Boimler's Number One poster a few times.
And? Each person can separate it however they like. There are no rules.