You can access PostgreSQL/PostGIS spatial databases without enabling them as an ESRI Enterprise Geodatabase:
"Unless you have specific needs for an ESRI Enterprise Geodatabase due to ArcGIS editing workflows, need for advanced geodatabase data types, relationship classes etc, you may be able to simply connect to the spatial database using ArcGIS Query Layersand not enable an Enterprise Geodatabase.
You just need to run the Add Incrementing ID Field tool against any spatial table in the PostGreSQL/PostGIS database if there is no suitable unique ID field for each record in the table. You will then be able to add a Query Layer including spatial columns to ArcGIS.
If your requirements are just "read-only" access of PostGIS data maintained by another software package, this setup may suffice.
I have run such a setup against large PostGIS databases with great success."
Source: Marco Boeringa at https://community.esri.com/thread/240840-arcgis-pro-create-enterprise-geodatabase-not-finishing