In ArcGIS Pro, open theAttribute tableof the feature class. Open theFields Viewof the layer. Rename the field of the feature class. Despite the maximum allowed field length is 64 characters (File geodatabase size and name limits—ArcGIS Pro | Documentation), it needs to be less to allow ...
When I run the script in the Python window of ArcGIS Pro it works just fine. When I run the script in an IDE like Spyder or Visual Studio Code sometimes I get the ERROR 100014 code; and sometimes it works. I am completely baffled why sometimes it works sometimes and not others....