I play TSW3 through game pass, i opened it yesterday and suddenly i was able to play Spirit of Steam, without having to purchase anything. Is this a glitch or was the TSW3 version on Game pass upgraded to the Deluxe Version?
It's not a glitch. The Deluxe Edition is free to play this weekend (Free Weekends games to try out) if you have Xbox Live Gold or Game Pass Ultimate. This includes Spirit of Steam in addition to the routes already on Game Pass/Standard Edition. After the free weekend, the add-on will stop mounting unless you decide to buy the route or an edition of the game with it.