How do big youtubers and small youtubers, Go around this. Issue.?

So what I'm asking is how is it possible to lower the file size of your video while keeping the quality? I was wondering because there are large youtubers such as MK, Fire and Ice. and small Youtubers that don't even have 1000 subscribers that are able to upload videos of their games well above the 12 hour mark at 4k sometimes going even higher than 20 hours. Of gameplay while retaining 4K.

There is a glitch in the system that allows you to upload videos of that length, but it doesn't work if the file size goes over 256 gigabytes. So that's what I'm wondering, how do they do it? To compress the file so much. Yet keep a high quality.

And I wanna also take this moment to say that it doesn't matter if your partner programmed. I've looked through different subreddits and some say it does, but for the majority, everyone agrees that it doesn't really matter. Especially when you have small YouTube channels that aren't even a part of the partner program able to upload 4K videos over 20 hours long. And that's my issue. I tried to upload a video that is at 2K, not even 4K. That was only 6 hours long. And it did not allow me to upload it. Due to the file being too large while prior I've uploaded A 5 hour video the same way and it worked. It was though, at 240 gigabytes. While the six hour video was at 260 gigabytes.