From a technical standpoint, it's essentially the sole edition with some updates; they merely rebranded it.
The Steam listing indicates the identical release date of August 18, 2020. The 40th Anniversary Edition is introduced as a free update for existing users, and for new purchasers, it appears under the name of the 40th anniversary edition from the outset.
You can see what updates they have on this website: https://www.flightsimulator.com/microsoft-fligh...
Is it worth it? Well, in my opinion, Flight Simulator is always worth it, hahaha. I genuinely enjoy the game and appreciate the realism it offers. The recent update, featuring the A310, has been particularly enjoyable; it's a fantastic aircraft. If you're unsure, you can check out some gameplay videos. I always find those entertaining, especially the ones that simulate realism with amusing ATC communications.