I'm not very tech savvy, but I have Googled a ton on this, so maybe I'm presenting the right details for the answer. Recently bought a Sony DSC-RX100 III which shoots optimally at XVAC-S 50p, and trying to choose the best render setting for YouTube in Movie Studio Platinum 13.0 (which I just upgraded to from 12.0).
When I set the advanced option filter to "Match Project Video Framerate" I get three Format options: Sony XVAC-S, Video for Windows, XDCAM EX. I choose the Sony version, and choose "XVAC S HD 1080 Long-GOP 50p" (there is another similar 4K option which is too large). This seems in keeping with the original file. I uploaded this to YouTube and looked pretty good (though there was one comment that said that it appeared slightly sped up, I don't see it though). You can see the end product here:
I have read that for You in general what I should be doing is choosing the Format Option "MainConcept AVC/AAC" and from there an option like "Internet 1080p".
As Youtube now handles 50p framerates it seems like what I'm already doing would be optimal, but I want to make sure that I'm not missing something.