You can sail close to upwind, but not completely. If you try to sail too much upwind, your boat is “in irons” and you stop getting any push from the sails. Because the sails aren’t pushing, you can’t steer either. Because of that, when sailors are sailing upwind and tacking across the direction of the wind, they have to make sure they have enough momentum to cross the path of the wind without stalling.

Meanwhile, in Sea of Thieves, if you get your sails set perpendicular to the wind you get bonus speed. If you get your sails 100% wrong (i.e. they should be pushing the boat backwards) you still creep forwards.

Honestly, I’d love a pirate / 18th century ship combat simulator that actually got the sailing mechanics more or less right. The mechanics of sailing are really interesting, and then you add artillery into the mix, what’s not to love?