Proof of work, even "custom", where the user does not need a particular interaction with the page, does not work. The scrapers are running headless Chrome and solving the work. They do not care, they do not pay the bill, the compromised system's owner pays the bill.

I have such system for the registration form on one of my website to prevent the double validation of emails to be used to spam emails of victims. The PoW challenge prevents less than 10% of the bots.