According to the website yowangdu.com:

"As of May 8, 2021, the Tibet Autonomous Region is open for foreigners currently living in China. (You will need proof of residence, a negative nucleic acid test, and a green code.) For now, Tibet remains closed to other foreign travelers."

and the "tour guide" as well.

Independent travel looks like it is not allowed. It looks the same as before the pandemic, but restricted to foreigners who live in China.
Am I wrong?