not sure about nextjs / vercel, but don't you have access logs for your webserver which you can check to see who's doing the cloning? Perhaps you can find some user-agent or certain ip-range or something is responsible, and block that.

there are tons of automated systems copying everything everywhere unfortunately. a lot are fairly ok to block.

There's also services you can hire or hosting providers who do some filtering for you, but those are generally more expensive than basic ones. (added security tooling around their platform)