I got the requirement, but it’s not actually possible. Plus having that screen isn’t a way to make a website more “secure”, it just means that less bad traffic will arrive. You, as a webmaster, should explain that it’s not really needed, will make a worse experience for the users, slow down loading, possibly lower a bit Google’s (and other search engine) ranking.
You could most likely have better security adding HTTPS (it will encrypt the connections, ideally between origin <-> Cloudflare <-> visitor if enabled correctly), enabling WAF (on the Pro plan), enabling Rate Limiting on the login/signup APIs or additional APIs that you have, making sure that the website is built and run on the latest software, enabling all the possible security features browsers now allow (CSP, SRI, etc.) and making it static if at all possible to prevent possible attacks on the backend due to bugs.
If you really still want that page to appear often you could simply lower the “Challenge Passage” dropdown in the Firewall tab of the dashboard to sometini like 5 minutes. Note that I STRONGLY ADVISE AGAINST IT unless you really know what you are doing and you have a really good reason.