MC version: 1.20.1
Fabric version: 1.16.3-1.16.5
Origins version: 1.10.0
Origins++ version: 2.2
Pehkui version: 3.8.3

A short time after loading a singleplayer world new or old, having pressed 'I know what I'm doing' the game gives a notification saying 'Connection Lost, Invalid Player Data' preventing playing singleplayer. It does however work without the Origins++ mod installed.
The Modpack in use is attached below.
Da Boys - Modpack (Fabric).zip