I recently tried to complete a spatial join in Pro 2.3.3 and because of the issues I encountered, I need to switch back to ArcMap to complete this task.
The attached file highlights the issues. In summary: field names from the Excel file were not recognized in Pro so I had a hard time picking the field I needed to conduct the join and all my data types became text when some fields are numeric data types.
ArcGIS Pro 2.4 brings big improvements in handling Excel. Please upgrade to 2.4 and it should resolve the field naming issue.
https://pro.arcgis.com/en/pro-app/get-started/whats-new-in-arcgis-pro.htm