Hello Irwin ,
Thank you for posting your question in the community and providing your findings with Path Tracer. At this time we tutorial showing how to get started with the Path Tracer and what settings affect what. I also recommend you take a look at the Demo scene found in Twinmotion and see how those are set up. I will mention to our team the need to have more documentation and tutorials for indoor scenes.
Path Tracer Tutorial:
https://youtu.be/XlFQ2HbiGvY
Keep in mind if you have a Skydome the lighting will be different and there are more settings to consider for your scene to look correct.
https://youtu.be/aPRWhyVa4k8
Try looking at increasing the Skydome and Sun Intensity, the Ambient Lighting setting for Skydome and Path Tracer, Max bounces for Path Tracer. Indoor scenes will look much darker if the space does not have many windows and adding light sources will be important.
If you have suggestions for improvements on Path Tracer/Skydomes you can make them on our official road-map:
https://portal.productboard.com/7pu88c9kpmqtzt8hwg6arujh/tabs/4-under-consideration
Hope this helps and if you need further help, you can ask from some advice from the Facebook group as users are often posting examples of their renderings and are happy to provide input. https://www.facebook.com/groups/twinmotion.community/
Kind regards,
Vincent B.