Party Limit Begone by Sildur:
https://www.nexusmods.com/baldursgate3/mods/327

Multiplayer Patch Installation:
1. First follow one of the mod installations up above. Then download the multiplayer patch and unzip it.
2. Drag and drop either your bg3.exe or bg3_dx11.exe file onto the PartyLimitBegonePatcher.bat file. It will create a backup for you.
3. That's it! Enjoy the game. Note: bg3.exe is used if vulkan is selected in the larian launcher and bg_dx11.exe if directx is selected instead.

Linux and Mac support:
PLB is supported by both linux and mac but the MP patch is tricky to install, the easiest solution would be for a friend to send you their patched exe file. Otherwise you must edit the PartyLimitBegonePatcher.bat file with any text editor and change this line: Set "GetFileName=%~n1.exe" to something like Set "GetFileName=bg3.exe" then place your bg3.exe file next to it - in to the same folder and run the PartyLimitBegonePatcher.bat file with wine﻿.

Console/Crossplay support:
PLB standalone works with console players if the hosting player is on PC. According to some users crossplay with more than 4 players works only via direct connect for the PC users.

Uninstall MP Patch:
Delete the patched exe file and restore your backup. The patcher creates a bg3.exe.backup (or bg3_dx11.exe.backup) file in your game folder, simply rename it back to bg3.exe. (or bg3_dx11.exe)