This never worked for me.
When I update ArcGIS PRO to a more recent version. All my python scripts stop working.
Then I try Package Manager>Upgrade an existing environment and it ALWAYS fails for me. I have to copy all python files MANUALLY from the default C:\Program Files\ArcGIS\Pro\bin\Python\envs\arcgispro-py3\ to my ArcPy old environment's folder like C:\ArcPY
Why?
(Esri, any plans to replace the hateful conda ems?)