I want to go to Tibet with a full-size SLR, with a budget of about 5-6 W. I want to shoot stars and scenery, and I want to set up a Canon, so I can ask God for recommendation.

If the budget is 50,000 to 60,000, it will still be 5D4, which is one third of the budget. You don't have to buy all three yuan, but I think you should have a favorite focal length, which is the maximum aperture.

Unless it is well controlled, the fisheye lens is quite lame.

Since your expected goal is wide angle, you don't care so much about large aperture, then outdoor lightweight multi-purpose lens can consider 28-300, basically full coverage, wide angle below. 5D4 plus 283 is only a little over 30,000, and the lens can be considered for wide angle. The rest of the backpack must be used. If conditions permit, the shelves and lights are good.