Do you have millions of viewers? With beefy enough hardware I’d assume you could, but not even the biggest streamers on Twitch stream to millions of viewers at a time. But that’s just gaming. I know that Owncast is leveraged by all kinds of folks for different purposes. Some churches use it to broadcast to their congregation, some weddings have done it, funerals, radios, local public access channels, etc.
I personally have a VPS on Hetzner, not sure about others. Obviously hosting is the thing. But I run a VPS for like $8/month, again on Hetzner, and I’ve done small live streams to about 15 people without much issue.