Quoted from reviews "One thing worth noting is that Netflix does not support HDR playback on the FE as of writing this - YouTube and Amazon Prime Video, on the other hand, do, so the phone definitely supports HDR, but it will be up to Netflix to enable the streaming support in HDR. The DRM Info app reports the phone is indeed capable of HDR10, HDR10+, and HLG playback, and it has Widevine Level 1." They need to support it. The hardware is there.
Neither Netflix nor Prime shows in HDR for me on the S20 FE. Youtube detects the display is HDR capable, but does not seem to activate HDR (e.g., by maxing the brightness). My guess is Samsung caught these content providers by surprise with the release of the S20 FE, so they haven't had time to certify the display and make sure it works correctly with their services.