How combat que works is a crucial part of the design for turn-based combat. Larian has been exprimenting with different systems.
Their previous game, D:OS2 would intertwine teams
one character at a time - one yours/one enemy/one yours/one enemy etc. That provided a nice regular pace between player and enemy turn, but allows for little interactivity between characters. And of course, is hassle free to coop play.
In the first
gameplay reveal of BG3 Larian tried something different - a shared initiative for each team with division into player and enemy turn, and in player turn player was free to move units in whatever order they want (so think XCOM games). From tactical perspective it is a more flexible system, though it has a downside of greatly favouring alpha strikes - who gets to go first has massive impact as they get to make a strike with their entire team, before the enemy gets to act.
After initial feedback, Larian moved to what we have now - a system very similar to the original table-top where each units rolls initative and combat que is build based on that, but they kept a bit of the tactical flexibility of their original system by adding shared initiative - so if multiple characters line up in the row you get "your turn" situation and you can act with them in whatever order is the most tactically useful. As a singleplayer gamer I like this system a lot.
I can easily imagine how it can be messy in coop. A more crude solution would be to add an option to disable this system (a bit like Civ games allow to set simultaneous/hybrit/and turn-based systems), but I wonder if being able to see your coop player's cursor could help as well - it might give players better information as to what they coop player's are thinking of doing. That said, such real-time feedback might need a decent connection, and I have no clue how good is BG3 netcode.
