"The following meta box are not available: "dealer_registration"
warning at the end of my login page only, and the warning stays there even after removing the login form from the page. I also don't have anything on my website called "dealers", or dealer registration. I tried to use the Gutenberg block and the shortcode for the form, but the issue is there with both options (and without the whole form as well).
The form must be added somewhere on your site so it displays in the frontend, maybe a custom code or Kadence block. You can try to deactivate all plugins except Meta Box, MB extension plugins and switch to a standard theme of WordPress and check this issue again.