Wrong Application MIME Type

I have been noticing this issue as well and nothing that I have tried seems to have worked (including the aforementioned patch).

For some reason, the podcast found at https://www.ccny.cuny.edu/presidentsoffice/podcast/feed is generating a content-type of text/html, which is causing a problem when I try validating it.

In my case the issue occurred only when caching was enabled (core < 10.2).

Using a core patch from this issue fixed it for me:

https://www.drupal.org/project/drupal/issues/3272985 🐛 RSS Feed header reverts to text/html when cached Fixed