To create a custom 404 page in Plesk Control Panel, follow these steps:

Step 1: Log in to your Plesk Control Panel.

Step 2: Go to the "Websites & Domains" tab.

Step 3: Click on the domain or subdomain for which you want to create a custom 404 page.

Step 4: In the domain/subdomain settings page, scroll down to the "Advanced Operations" section and click on the "Error Documents" option.

Step 5: Click on the "Add Custom Error Document" button.

Step 6: In the "Error code" field, enter "404" (without quotes) to specify the 404 error code for a page not found. In the "File path" field, enter the relative or absolute path to the custom error page file. For example, if your custom 404 page is named "404.html" and located in the root directory of your website, you can enter "/404.html" as the file path.

Step 7: Click on the "OK" button to save the custom error document settings.

Test the custom 404 page, try accessing a non-existent page on your website. The custom 404 page should be displayed instead of the default server error page.

That's it! You have successfully created a custom 404 page in Plesk Control Panel. Make sure the custom error page file exists in the specified location to ensure it is correctly displayed when a 404 error occurs.