please give actual examples/links to solutions (with a spoiler flag) of things that should be banned, otherwise we cannot do anything

Node versions will not be restricted. The point of the kata is to implement the algorithm yourself, this is why it is 4-kyu, if you do not want to do that, skip the kata. It is a known issue that the JS version is not cheat-proof (see issues below). Completely disabling a built-in is very hard on Codewars, this kata should never have had a JS version to start with. Hopefully someday the JS version can be nuked, but I believe it is not currently possible to do that.

It seems reading the file won't work anymore, could you check it?

It's worth a try, let's see. It messes up with chai, but I'll look further into it.