Redirect to 404.php not working

Have you re-saved your permalinks?
Are you using apache?
It should work by default, but maybe you have some permission issues going on with your server.
https://www.wpbeginner.com/wp-tutorials/how-to-redirect-your-404-page-to-the-home-page-in-wordpress/

Adding 404 to your htaccess file in apache is pretty straight-forward:
https://httpd.apache.org/docs/2.4/en/custom-error.html

Maybe mod_rewrite is not enabled?
https://www.digitalocean.com/community/tutorials/how-to-set-up-mod_rewrite#Section%201

Hi @corrinarusso, yeah we tried all that but it just doesn’t work ??
We use a LiteSpeed server. We have a 404.php file and I tried the htaccess change, but it won’t work. Mod_rewrite is enalbed, because we use it for other things in htaccess.

We are a bit lost. Any chance you could help us out?

I would ……..
– check your ‘apache’ error logs
– backup your existing .htaccess
– upload the default WordPress .htaccess :
https://www.ads-software.com/support/article/htaccess/#basic-wp
– re-save your permalinks
– test to see if WordPress and 404 works as expected
– go back through your existing .htaccess and add things back into the default file

Ask here instead:
https://www.reddit.com/r/servers/