With D:OS1&2, each platform version uses that platform's multiplayer API, and on PC there is Direct Connection and LAN for Steam / GOG / App Store multiplayer.
For BG3 there should be details about multiplayer announced closer to EA/release.
Right, so ignoring consoles, MP uses a player PC as host instead of a public server, allowing you to connect any other PC player you can reach.
I suppose that could be extended to include Stadia players for BG3, but would probably not be using Stadia to best effect.
Thanks.
