The PostgreSQL 11 is not supported or "compatible" with 10.8.1 ArcMap, ArcServer or Arc Pro 2.7. For the ST_geometry file download is a simple solution and can be found under Arc Pro 2.8 in My Esri, but making the upgrade for PostgreSQL to be compatible with 10.9 and 2.8 for Arc Pro has proven to be a challenge.
PostgreSQL 12.4 no longer supports the OID columns in PostgreSQL 11 and will throw a lot of warnings once the install of PostgreSQL 12 is installed and you begin restoring the databases.
I have gone through quite a few variations of the steps for this upgrade including doing it all through command prompt, using pgAdmin4 and dBeaver, all having errors or failing to allow connections to the database from the database connections in Arc Map, Catalog, or Pro.
Once I get it figured out completely I'll post the solution but so far making the upgrade happen has not been an easy process. If anyone has the order of operation or the combo to unlock the secret of this upgrade, do tell! Otherwise stay tuned.