Thanks. All good. In my tester app I installed the postgres assembly via package console against .NET Framework 4.8:
I then ran into:
ORMGeneralOperationException: None of the factories in the list of 'Npgsql' were found. Please check machine.config and the .NET version your application is running on.
So used the redirect in app.config
<add name="PostgreSql Client Data Provider" invariant="Npgsql" description=".Net Framework Data Provider for PostgreSql" type="Npgsql.NpgsqlFactory, Npgsql, Version=188.8.131.52, Culture=neutral, PublicKeyToken=5d8b90d52f46fda7" />
.. with the gotcha that the .config file didn't get regenerated in my debug folder after compile, which confused me for a bit. Classic Visual Studio.