Regular people on YouTube wouldn't notice much of a difference - especially if post is fancy - but there is if you know what you're looking for...the better color, the micro-contrast, less artifacts from the higher-quality formats, the robustness for grading, etc.
If this was going from like a $1000 Canon to a $4000 Canon I would say probably not worth it if you're already shooting with such a consumer camera and getting by just fine, but in this case the extra money for a GH6 isn't that much and you're getting a variety of other features the G85 doesn't have, including what might be Panasonic's best AF camera so far (but not as good as systems from the other big 2).
It's definitely an upgrade, especially if you're shooting in prores and vlog. However, my gh6 has been a regret for me personally due to the streaking issue. Honestly I would rent the gh6 for a week and see if the camera fits your needs. For me, I shoot for a hunting show often and would keep my gh6 in my bag for the 4k120p slo-mo stuff or if I wanted the extra reach out of a long lens. But honestly I've been burned on beautiful sunsets one too many times.