The first cutscene of the campaign is kinda a very quick summary of the relevant events of the past few expansions. There are videos made by popular content creators online that cover the story in more detail (you don’t need to watch the 10 hour one, other content creators have made shorter ones).
There is an in game timeline, which tells you the general plot in 2 or 3 sentences and allows you to play a short mission from the DLC. You can find in the director on the top right.
Seasons are excluded though so the best way to get up-to-speed might My Name is Byf recent 'story up to final shape' video. Its 10 hours long, but the description has timestamps for the revent seasons so you can skip around.