According to the GeoMedia Smart Client 2020 realse guide, the system requirements is to have 12c or higher DB server. Does this statement have been checked against Oracle version 19c?
Both Oracle 18c and 19c are internally versions 12.2. The first one being 12.2.0.2, the other one 12.2.0.3. Therefore, apart from bug fixes and Oracle's long-term support perspective both of those versions should act the same. I don't think that we tested 19c in particular, but we surely support 18c version.
Just keep in mind that the client-side installations differ between 12.1 (12c) and later versions:
