[tabbytown]

Supposedly they'll turn it down if it's mastered louder than -14 LUFS. They won't turn it up if it's quieter.

I couldn't find a Youtube source for this but it's mentioned extensively online: https://audio.rswaver.com/blog/youtube-loudness-standards

[topranks]

You “turn it up” by using dynamic range compression. Which is fundamentally altering the work.

It’s right and proper YouTube do not do this to people’s work.