https://attackofthefanboy.com/guides/how-to-create-custom-party-members-in-baldurs-gate-3/As title says. It is no longer possible for me. At the third instance I got always a crash...
Please finally add a character creation for custom parties WITH character export function. Character import would make it easier to quickly load created chars for a custom party. At the moment you have to painstakingly recreate the characters every time and it is precisely during these creation processes that a crash occurs.
Edit: Before trying it I had deleted (all folders also under appdata) and reinstalled BG 3...