If you bought it on the MS Store for PC, I believe you don’t have access to the XB Version (not 100% sure), but if you did instead buy the XB Version in the XB Store, you can also play the PC Version for free. This is a Play Anywhere Title. You don’t need any Game Pass. If you want to play Online with friends, you need XBL Gold (not Gamepass!), which costs about 60$ / year. GamePass Ultimate includes XBL Gold, while the normal Game Pass doesn’t. Game Pass is a gaming flat line abo you can play the games in it (FS ist one of them) as long you pay the abo.
So the question is, is the Play Anywhere feature still so, that games bought on PC MS Store, are only playable on PC or not. If you are able to download the Game in XB Store for free with the same gamertag as on the PC, than everything is fine and you don’t need anything further. If not, you must buy it again on the XB or buy the game pass abo and pay every month money to play FS from the GP. To play Online with firends, you need only XBL Gold and NO Game Pass abo, I you bought it again on the XB.