Lack of standard design to show wrong URLs or pages with errors

I have discovered that NC cannot treat the wrong URL, in particular:

1. https://mydomain.tld/1 leads to the error Page is not found preserving theming in full. That is FINE.

2. https://mydomain.tld/1.php leads to the page with just a wording File not found without any theming and UI elements. So, this relates to any absent php files.

3. https://mydomain.tld/remote.php leads to the page with the error Path not found without theming but preserving the elements

4. https://mydomain.tld/remote.php/dav/user/ leads to the page with the error Page is not found with the default NC theming (no logo and background are kept).

5. https://mydomain.tld/remote.php/dav/files/not-loggied-in-username/ leads to the page with warning This is the WebDAV interface. It can only be accessed by WebDAV clients such as the Nextcloud desktop sync client. without keeping any theming.

6. https://mydomain.tld/remote.php/dav/files/lgged-in-username/ leads to just a blank page. Here should be some themed warning that you have to use your webdav client to access the data, please go back to your homepage, whatever.

7. https://mydomain.tld/remote.php/dav/contacts/username leads to the page with Sabre errors without any styling.

8. When updating/upgrading the system the logo and the background changes to the default Nextcloud, so not preserving the theming in full.

Is it possible to fix unique design/theming across all pages?

Reproduce the listed URLs, including missing paths, WebDAV endpoints, and upgrade pages, and compare their error responses and theming. Trace where each response is generated and identify the existing themed error page to use as the reference. Done means the affected cases consistently show the intended Nextcloud theming and a clear user-facing message.