Hey you guys!
Sorry for my late response! I have another Update already:
We could solve the problem with the mime types:
we are using Cloudflare in this example and it seems like that the Proxy (enabled because of SSL validation) is not transferring the mime types correctly. By setting an Transform Rule with the following expressions, the error with the mime types disappeared completely.
Still, talk is not loading in our nextcloud web application and is throwing another error:
Though, it seems like a cloudflare proxy problem - by disabling the proxy for this host, everything works fine after some waiting time. I’ll investigate this problem a little bit more further.