Additional info to John's answer. Make sure you check following before proceed with John's answer.
Make sure to remove Post Proprocessing Stack V2 (PPv2)
Go into Window -> Package Manager, Select "In Project" and search for "post processing" package like this one in the screenshot. The PPv2 package is for built-in renderer not for URP. You must delete it to prevent confusion.
This is common pitfall if you created your project as built-in renderer then decided to switch to specialized renderer later (URP, etc) your project might be having this package installed.
Notice that component icon from 2 packages are different:
And lastly remove your post processing profile asset if it was created with PPv2. The URP one has its own different asset and cannot be interchanged.