Hello!
You can actually use the UE4 sky_sphere in UE5 to gain access to the clouds (not the volumetric clouds) and the stars. in order to do that, you need to go to settings in the content browser and enable “Show engine content” and search in the “all” folder “Sky_Sphere” and it should appear the sky sphere blueprint as in the UE4 engine. you have to delete the current sky sphere in order for the new one to work.
if you want to change the speed on the volumetric clouds the answer is in the following link
Hope this helps!