I don´t know, games like PoE2 made the two modes, and you can play Pathfinder kingmaker in TB or RTWP with a mod. Owlcat studio already announced that they will allow two gameplay modes: RTWP and TB in the upcoming PF: WotR...

But to be fair those games do not have online multiplayer mode, so it is unlikely that BG3 would have that option from the start.