What exactly is season level?

Hello all, probably a dumb question but I cannot understand what this level showcases.

I came back to the game for the anniversary update after 3+ years, from activities I get both xp for the anniversary pass which is almost done and then this season xp. Is there another general season pass menu with rewards that I'm too blind to find or do I need to get Brooklyn DLC?

Thanks!

https://preview.redd.it/5keyrm0x1vng1.png?width=1161&format=png&auto=webp&s=3c73acdb495d005f34658a697c694cfa6550a7c5