Hello everyone,
I own the game on both platforms, Microsoft and Steam. In the past I had to uninstall the Steam version to force the Microsoft one to open when accepting invites or I had to use Xbox Companion App to find my friends profile and join via the Join Game button (the button no longer shows up).
Since this update, even if I uninstall the Steam version and close Steam client, everytime I accept any invite it just launches my Steam client and a Sea of Thieves installation pops up. I don't know what else to do (except uninstalling Steam completely).
One workaround I found is that I can accept on mobile (xCloud), join their session, quit forcefully and then launch Sea of Thieves on PC and rejoin that session. But it's tedious.