When the hypervisor CPUID bit is set, the Display tab is missing in Radeon Settings. In addition certain other features are also missing (notably Enhanced Sync)
Hiding the hypervisor flag and doing a Clean Install is a workaround, however there is a significant performance impact in certain scenarios (in particular latency-sensitive workloads).
There was another workaround back around version 17.7, where the 32-bit Settings application would have the missing Display Tab (still no Enhanced Sync, though). However, since the removal of 32-bit support, this has no longer been possible.