Okay so, I've tried following the encoding tips as much as possible, even now posting things with a crf of 15, but my issue lies with the color settings for Avidemux.

In the guide on the site, it says to use "Output 2" in the Configure settings, but the thing is, Output 2 is not even accessible to change: https://imgur.com/a/VMtp6MZ , and there is no guide either here or any other site that says how to make it accessible. So I'm just wondering how to do so.

I just checked the version of avidemux that I use (2.7.6), and I also don't have that option. It most likely just isn't possible on the version you're using because the backend doesn't support it.

I installed a newer version to compare (2.8.1) and the Output 2 settings were accessible. I would recommend installing a newer version if you were using an older one like me.

yet the newer ones have a weird issue to slightly randomize framerate when decoding

thankfully that's only a cosmetic error, which is still annoying tbf, but it doesn't actually change the fps of the video itself