If you get motion sickness after 20 minutes of a seated experience that is running at full frame rate, with no artificial locomotion, you are decidedly in the minority. It is not impossible, but it is far from common.
Not all - beat saber you're still, workrooms meetings you're still.
Sim Racing, any game where you fly or run around - those are artificial locomotion and can definitely take some getting used to for some (not all) people.
Everyone I know has a cap of around 20 min for their VR experience, some for motion sickness, some headaches. It's a small sample size of just people I know, but it's significant enough to mention.
