Look at the screenshot from the link. It seems like the clouds is laying on the ground with straight lines. Serious glitch that would make flying in cloudy weather a no go. Is default XP11 that is so bad ? If so are there some add on that can solve it ?

https://1drv.ms/u/s!Ao8G1zqCjqI5jC26XDXrMlA0v_nx?e=R7a5UA

 

Try with the vivid sky v1.1 package
Or create a lua.txt file with the entry:

set ("sim / private / controls / clouds / check_z_hdr", 0.0)

(FlyWithLua plugin required)