When trying to connect to SDE, some GIS editors might get the following error message in ArcGIS Pro:
Error: Connection was attempted with an older version of SQL Server client communications software that is not compatible with the SQL Server database server
On the user's machine, open Settings > Apps & Features in Windows. Scroll down to the M's and see if there is an ODBC Driver present:
More than likely, there won't be one there. To fix this problem, you will need to download and install the latest SQL ODBC driver. We have it ready to go right here: \\GISFS1\GIS_SHARE\Installations\ArcGIS\ArcGIS 10.7.1\Desktop\ODBC Driver
Double Click the file there or simply double click the SQL ODBC file that is attached to this article.
Install the ODBC driver and you should now be able to connect to the sde database in ArcGIS Pro.