Select quest mode when you arein the menu quest headsets dont use base stations and thair origin point stays where your head is that's why quest mode exists in the menu
I am developing the game with a Valve Index and a PC, so I see no reason for you to have issues. The VR mode is the one you need to select; it uses the OpenXR VR environment supported by Steam.
I have noticed this issue the problem is that it happens to random people I have people with the same devices experiencing different results both have a quest 3 with the same settings and with up to date software if you have payed for the game go ahead and request a refund
download the stuck in ground version it's made for people who get stuck in the ground, or you can put your headset on the ground when launching the game and your hight gets calibrated