Hello, it seems indeed that there are ongoing issues in Ps 2020 with 3D, the best we can recommend is to post in https://feedback.photoshop.com, with examples of problems, and invite your peers to chime in through forums, social media, to raise attention about those discussions. The more pertinent information, the better it is for the Ps Engineers to be able to fix it...
I can confirm that there are issues. The material system has been changed to a PBR Metallic/Roughness workflow which matches the Dimension (and many other 3D apps). Unfortunately it also seems to have brought bugs including black GPU preview or in some cases inverted GPU Lighting - where the shadows are light and the highlights dark.
The issues are also impacting Lighting effects renders and spherical panoramas, all of which use the 3D engine.
Some have had success with a preference reset and I am currently able to use 3D with NVIdia driver 441.66 but it is far from perfect, the materials do not yet work the same as Dimension.