Yeah fun fact I actually looked this up a few days ago in the wayback machine because I own a beta account. Back then it was just Notch selling the game and the "agreement" if you can call it that on the site basically just said "you own the game forever, no drm".
I'm not a lawyer or anything but I suspect that unless they somehow tricked users of old mojang account to agree to Microsoft TOS after the purchase of Mojang what Microsoft did may be very legally questionable. But the main issue is who is gonna sue them over 20 bucks. They know they can get away with it
Open office has been dead for years now. The core team moved to Libre Office