This reminds me of something I find myself constantly explaining to colleagues again and again: You can scale a monolith in its entirety to handle elevated traffic in one of its "subsystems"; having code paths that aren't receiving traffic doesn't cost anything (at least in the architecture of the systems I look after).

I don't see the value in separating a monolith to allow independent scaling, unless there are wildly different performance demands across its components which makes reliably autoscaling difficult.