JohnWayne111 just talked to RPi devs but you might not like the answer:
RPi4 doesn't have hardware support for HDR-to-SDR tonemapping, it might be possible to tweak things a bit but the result will always be off - either too dark or too light.
Simple solution: don't use HDR encodes if you don't have a HDR display.
You could also try to re-encode the HDR files on your PC, ffmpeg (and probably other encoders) should support that with tonemap filters (never used that myself though).
so long,
Hias