As you are probably aware all tourists travelling to Tibet need to join a tour for their stay. The tour company needs to be registered with the Chinese government. The tours are on the expensive side making it an expensive place to visit, especially if you go during summer when demand picks up.
You need to get a visa to travel to China, then you need to apply for a travel permit for Tibet.
I can only imagine Covid seriously impacted tour companies in Tibet. I would do the usual due diligence before booking, such as checking online reviews for the company. Obviously, you would want to go with a company run by locals.
Here are a couple of companies I saw recommended by a few people.
Tibetan Guide is your trustable travel agency boutique in Lhasa. We offer tailor-made tours and local travel guiding services across the Tibetan Plateau. We have our own tourism license and authorization to apply for Tibet Travel Permit without any intermediary.
www.tibetanguide.com
We have dedicated ourselves to offer the best value Tibet tours since 1984. Tibettour.org is set to help you find first-hand information on Tibet culture, transportation, weather, permit, and accommodation more conveniently.
www.tibettour.org