Welcome!
To date, nVidia has been more interested in protecting their intellectual property by concealing details of their hardware rather than opening up specifications to third-party concerns. The OpenBSD project refuses to incorporate any third-party binaries into their kernel which they cannot audit and improve. Since both sides have conflicting goals, we will likely continue to see marginal support in OpenBSD. If you can find another video card which is supported, your user experience will likely be far more more enjoyable.
The general rule is to avoid nVidia whenever possible.