When the RP4 got released earlier this year, 15Khz RGB solutions like the RGB-Pi and Mike Chi’s RetroTink Ultimate were deemed unusable. The GPIO connector was still on board but the DPI seems to be different from previous models, making both hats incompatible with the newer Pi.
As demonstrated in the video, the RGB functionality can be restored through a slight alteration of the config.txt file. Bahn Yuki used the following settings to get the Retrotink Ultimate, specifically, to work properly, in his case, through YPbPr:
hdmi_timings=3840 1 109 343 343 224 1 19 3 16 0 0 0 60 0 7292529
The LibreELEC based Lakka 2.3.1 running Final Burn Neo looks to be performing pretty well on a CRT when the new settings are applied.
This, in my opinion, is awesome news for RetroTink Ultimate owners, as the RP4 is a much more powerful device than its predecessors and can be used to exploit previously unattainable emulation (RetroArch) features like the infamous “runahead” mode.