Personally, I strongly recommend not to fly directly to Lhasa!
First, there is not much to play around Lhasa, and the tour is completed in three days at most. Second, I&;m afraid you can&;t adapt to the altitude and have a high reaction.
I traveled from Chengdu to Lhasa for 23 days in April this year.
Life must experience a self-driving Sichuan-Tibet line.
The best choice is to fly from Guangzhou to Kunming/Lijiang or Chengdu. Then rent a car and take the Yunnan-Tibet line or the Sichuan-Tibet line.
D1 recommended Lijiang for the longest remaining time. Car rental in Lijiang, one day to Deqin, you can see Songzanlin Temple in Shangri-La and Rizhao Jinshan in Meili Snow Mountain.