Remember, this is the Divinity engine. This is most likely due to a restriction of the engine used and will not be able to be changed.
Bogus. Not only there’s no “engine restrictions” in place (how do people even come up with this stuff when it doesn’t make a lick of sense technically speaking?) but the game does support party of six characters already by save file editing.
And yes, the UI scales appropriately too.
And no, that’s not an ideal solution, which is why we are asking for proper official support.
Party control in Baldur's Gate 3 is a complete mess that begs to be addressed. SAY NO TO THE TOILET CHAIN