I’m pretty sure most spam senders black hole any response, the money is in the target clicking a link and no where else.

Don't most of the "nigerian-prince" type scams involve some kind of back-and-forth?

Using a link to a website to start the process

I get a number of spam emails with no links. Just plain text, wanting a back and forth.

I suspect that’s more an attempt to warm up a domain/ip or something. Manually replying to emails wouldn’t scale

Hmm. I confess I don't often go into my spam folder but was just going from what I recall of the back-and-forths on https://www.419eater.com/html/letters.htm

Look up 'pig butchering' when you get a chance. It is an elaborate process of convincing your mark to fall in love with your persona and asking them to send it money. It takes months to years to execute but marks end up losing their properties, retirement accounts, life savings, everything to it.