Thank you for the great question Afif.
Error pages are a feature of IIS, and you can configure that within IIS manager.
For example, if you wanted to edit the page being called for a 500 error, you would do the following:
Launch Internet Information Services (IIS) Manager
Expand Sites > Default Web Site, and then select ESD
In the Features View, under the IIS section, double-click Error Pages
Under the Error Pages details, double-click the entry for the 500 error
Choose one of the following options: Insert content from a static file into the error response; Execute a URL on this site; Respond with a 302 redirect
Configure the option you wish to use, and then Save that change
This will require a server-side edit, but it is a one-time configuration.
For errors within the website itself, App Portal does provide an error page, which the administrator can edit. To view and modify this page, perform the following steps:
Navigate to the Admin page
Expand Site Management > Communication > Notifications
In the Global tab, double-click the Error Message Display notification
Edit the notification as needed, and then save the change.
Hopefully this helped!