Answer 1

Point route of root with any query string to the custom 404 page.

What's the backend tech stack of your website?

Answer 2

Do you use frameworks like reactjs, angular , vuejs or nextjs?

You can very easily setup 404 page javascript frameworks.

I don't know how to setup 404 page with Vanilla javascript.

Answer 3

https://stackoverflow.com/questions/45619407/how-to-create-a-404-component-in-vuejs-using-vue-router