Hello, just to provide some clarity to this.
Season 4 is absolutely a part of Year 1. In terms of the future for Battlefield 2042, we have recently stated that we will continue to support the game in the form of Season 5 which takes place after the final season of Year 1.
We look forward to chatting more about Season 5 as we move closer to that time, but for now - we've just launched Season 3 and we're now working towards Season 4. One step at a time! :)