This error usually means that there is not a TNS file available or the entry for the DB is not in the TNS file.
Where is the TNS file located?
Can you provide a screenshot of the connection window in Pro?
This is the db connection, image attached.
I have Instant Client under:
I have tnsnames.ora under:
I have st_shapelib.dll under:
C:\Program Files\ArcGIS\Pro\bin\x64 and C:\Program Files\ArcGIS\Pro\bin\x86
Do I need to add path in Env??
Make sure that the Instant client is 64 bit. Then follow the information here on the environmental variables: https://support.esri.com/en/technical-article/000012021 just replace 32 bit with 64 bit.
That should get you going