Dune and Zidoo have been false-advertising FEL support for a while now for S928X-based boxes, or even S905X4 on the Dune OS & Android sides.
Look at how Dune sneakily frames FEL–I highlighted the statement in question :)…
Dolby Vision profile 7 FEL
The media player supports direct playback of Dolby Vision profile 7 FEL double-track and double-layer files. This is the most advanced Dolby Vision format. The media player plays video in this format using both tracks/layers. The important Dolby Vision information from the second track/layer (Dolby Vision RPU metadata) is transmitted to TV together with video data from the first track/layer. The passed video data uses 10-bit color depth - the maximum color depth supported by OLED-panels in OLED TVs, i.e. this fully uses the capabilities of OLED TVs. Combined with the full use of Dolby Vision metadata this gives an excellent Dolby Vision picture on the TV screen.
What they really mean is the RPU metadata from the enhancement layer is transmitted to the TV together with the video from the base layer.