TL;DR Upscale your export resolution to trick YouTube into using its better codec when encoding your video. Increase your export bitrate according to your new export resolution.
It is my understanding that YouTube will always re-encode your video with the h264 codec regardless of your upload format. From this point, depending on the popularity of your channel, it will decide whether or not to additionally encode your video with the vp9 codec. The vp9 codec is said to provide better resolution than h264 without increasing the required bitrate (doesn't extend buffer times). Read what YouTube have to say about it here.
To check which codec has been used on any given YouTube video, right click then click Stats for nerds. Doing this on your video yields this window:
We're interested in the following line: Mime Type: video/mp4; codecs="avc1.64002a"
codecs="avc1.64002a" means that your video was only re-encoded by YouTube with the h264 codec. Although YouTube has not deemed your channel popular enough to earn vp9 by default (join the club), it is still possible using any of the emerging methods.
Of the few methods I've come across, the most consistent is to upscale your export resolution to 2k (2560×1440) or 4k (3840×2160) despite the source footage being of presumably 1920×1080. This forces your video to be re-encoded in vp9 following the initial re-encoding in h264. This means that if you upscale your video, upload it to YouTube and promptly check which codec it has used, it will list "avc1.64002a" until it has finished processing in vp9. When you have successfully attained the vp9 codec on your video, the window will read:
Mime Type: video/webm; codecs="vp9"
Although I stated earlier that the vp9 codec itself does not require a higher bitrate, using this method does. This is as you are upscaling to a higher resolution in your export - not because of the codec. The recommended upload encoding settings provided by YouTube here state that the ideal bitrate for 2k and 4k videos is 24 Mbps and 53-68 Mbps respectively. The bitrate you decide on will depend on your internet speed and patience, both for upload time and re-encode time. From my personal render tests, increasing the bitrate significantly beyond these suggestions provides little return.
Don't be confused by the upscaling; a vp9 YouTube video being watched in 1080p60 will still look better than a h264 (avc1.64002a) video being watched in 1080p60.
Sorry for turning this into a huge text dump, I wanted it to be as complete as possible to avoid an influx of queries. That being said, its fairly late for me rn so if what I've said doesn't make sense then ask for clarification.