Don’t put it in the root folder (/) put it in its own folder like any other page.
Every RW page has an accompanying folder that contains the css/js etc for that page, if you publish 2 pages to the same folder (root in your case) you’ll get conflicts.
So, I have been on the phone with NetworkSolutions, my hosting site, and they will not be updating to php 7.4 as it has not even been released, according to Wiki.
If 4xx error stack does need 7.4 then I will have to wait.