Hi ,
In the new UI in 2023.1 Preview 2, the Reflection parameter for materials has been replaced with the Roughness parameter. You can adjust the Roughness of a material to achieve everything you could with the old Reflection parameter. The only thing to take note of is that Roughness is the inverse of Reflection, so a Roughness of 100% is equivalent to a Reflection of 0% in the old UI.
Best,
Raghib