Hi ,
The Reflection parameter of materials in older versions of Twinmotion has been replaced with the Roughness parameter in the new UI from 2023.1 Preview 2. Functionally, the slider should accomplish the same things as it did before. The only thing to be aware of is that Roughness is the inverse of Reflection, so a material with 80% reflection in the old Ui should have 20% roughness in the new UI.
Best,
Raghib