Hello app dev,
For 25, we have significantly changed the style of the guest/login pages (see Redesign guest pages for better accessibility by CarlSchwan · Pull Request #33265 · nextcloud/server · GitHub). If your app is providing some public pages, please make sure to adapt it to the new style.
In practice, it only requires, wrapping your existing UI with the following code:
<div class="guest-box">
// existing code
</div>
This should be backward compatible since the .guest-box does nothing for earlier versions. Talk, Calendar invitation, and the registrations are already ported.
If you have any questions or need help with adapting your code base, feel free to reply here 
Cheers,
Carl