I can share a web layer to ArcGIS Online from ArcGIS Pro with no problem. However, can you overwrite a web layer using ArcGIS Pro? Everytime I try, I get a message that I have to select a new, unique name. I could do it with Desktop. Thanks.
I believe that this doc (specifically the Over-Write section) says that you can only overwrite data with a shapefile or feature class. As stated, the name and (ideally) the schema cannot be altered. I have not used Pro, but it seems from the problem description that you are trying to overwrite a web layer with a web layer. Is that correct? If so, then this might be a current limitation. An idea on Ideas Portal would be nice.
Overwriting/updating web maps, web scenes, and web layers has not been implemented in ArcGIS Pro. This functionality will be available in a future release.
