Detailed Blog https://blog.kiprosh.com/show-custom-404-error-page-for-netlify-applications/
This Repo demonstrates issue with Netlify routing and a simple hack to fix it.
for redirects
[[redirects]]
from = "/*"
to = "/error"
status = 404
Netlify should redirect user to /error for any route which is not found but for routes starting with /error (starting with to path) i.e
/error__
/error*
Netlify still shows its default 404 error page. We can fix this issue by creating 404.html and adding following code to redirect user to error page
window.location.href = window.location.origin + "/error";