Wrong rendering from api

[nils-trustnode]

Steps to reproduce

1. Open any Google Calender Invitation in mail app

Expected behavior

Clicking any of the provided buttons should trigger the html link.
The hyperlinks in textform are working like expected!

Actual behavior

The buttons are not clickable at all.

Mail app version

3.7.17

Nextcloud version

29.0.2

Mailserver or service

No response

Operating system

Linux 5.15.0-128-generic x86_64

PHP engine version

PHP 8.3

Nextcloud memory caching

No response

Web server

Apache (supported)

Database

MySQL

Additional info

By investigating the iframe message content, I was able to find the address from the api: index.php/apps/mail/api/messages/262/html
Opening the URL separately (not in an iframe context) shows the same behaviour, therefore I assume the problem is in the processing part of the api.

[nils-trustnode]

Couldn't resist testing the newest version, but it's exactly the same behaviour on version 30.0.4 with mail 4.1.0,