What’s clear from the teaser is that the coming season is set in an alternate timeline, and messing with time is well within the capabilities of the extra-dimensional alien Q. He has done so on numerous occasions during the series, mostly for his own amusement. For example, in the Season 6 episode “Tapestry” on “Star Trek: The Next Generation,” he shows Jean-Luc Picard an altered future in order to teach him a valuable life lesson. He displaces the captain through different time periods again in the series finale “All Good Things,” doing so as a test of humanity.
He even states to Picard in the teaser, “Welcome to the very end of the road not taken,” making it clear that these time-bending shenanigans are of his doing. As to the motives behind Q’s actions, it is anyone’s guess. However, it’s not just Picard who is affected by this. Numerous characters seem shocked to find themselves in an alternate dimension where nothing is as they remember. So let’s see who else is caught in Q’s time web and what changes we can spot.