The openclient is not open enough. The .Net proxies to PASOE can only be used from within a .Net Framework assembly.
Please allow them to be fully compatible with .Net Standard so they can be included in assemblies that run on either the .Net Core or the .Net Framework. Even WinForms and WPF are going to be running on .Net Core soon, so I don't see why the "openclient" is not able to do so.
(As an intermediate measure, please continue targeting the .Net Framework but simply remove any references to unnecessary API's which aren't available in the .Net Standard 2.0. Why do you have references in there to OleDb ??? )
Here is a link to the allowable API's in .Net Standard 2.0. It is very rich, although it doesn't include OleDb.
Here are more details about the need for an openclient that is more open: https://community.progress.com/community_groups/openedge_development/f/19/t/56089
Please consider doing this work in version 11.7.x. It will be a long time before some of us are ready for OE 12. (For example, some of us have to first migrate away from the HP-UX platform which is being retired.)