[Sparktank]

What is your source?
There's still a wide range of info you are not giving.
Mediainfo isn't that useful.
I'd rather trust FFprobe, since that's how FFmpeg will read it.
They both rely on different processes, so go with the one that will be processing it.

Why -color_primaries smpte431 ?
I largely suspect this is why you're getting that HDR look if you were to work with a UHD-BD that has HDR10.

Make the primaries 709 like the rest.
Whatever the source is, if you convert to 709, you'll get the proper pictures. Unless the player you use can do 431 properly.
If FFprobe shows everything is 709, don't force smpte431.

If it truly is an XYZ colorspace source, then converting it to any other format should turn out alright when you watch in something like MPC-HC with MadVR as the renderer. I don't know about any other player.


Lastly, I know a lot of people come in here from torrent sites that copy settings from some random encoder, expecting those to be the one-for-all encoding settings.
X265 is not really needed unless you have HDR to work with.
OR want hardware playback compatibility.
I just suspected you copied some random setting that's useful for HDR encodes and applied to an SDR encode (since no info was really given).

Otherwise, you can achieve better transparency with x264 (that's been around for centuries).