What bugs will be fixed in the final release of SU11 (Sim Update 11) is something we will see. What the 40th Anniversary Update is, is basically a content update with new aircraft, helicopters, gliders and activities.
Both the 40th Anniversary Update and SU11 will be free and mandatory for everyone, on every platform (Xbox, Steam, Windows Store, Game Pass). The updates happen automatically as you turn the Xbox on, it finds the update and downloads/installs it.
When you start the sim, it may also update content in-game, it will be useful to go into Content Manager and update everything that can be.
Whether SU11 (the “bug fixing update”) and the 40th Anniversary (the “content update”) arrives on the same day is not 100%, but it has a high chance. November 11, 10 AM PST.