Hello,
If you upgraded within last 10 days, you can downgrade back using this guide:
https://www.kapilarya.com/how-to-downgrade-from-windows-11-to-windows-10
Once 10 days limit is reached, you need to make clean install of Windows 10, if you still want to go back.
Let us know if this helps!
Note: Included link in this reply refers to blog post by a trusted Microsoft MVP.