Anti-trust wouldn't apply here because there is very little stopping someone from creating a video hosting company and doing fine. Plenty of alternatives exist as well here, Tiktok, Vimeo, Twitch, Patreon all to varying degrees of scale.

Where I would try to nail Google/Youtube for with anti-trust is the merging of Music and TV/Movies into Youtube as well as the reliance of Google ads on Youtube. Both of those are incredibly annoying to deal with as a competitor and give Google the ability to corner the market on multiple fronts. Roku has highlighted this themselves, Google leveraging Youtube to make brand deals that other competitors cannot.