Hi Dani,
I'm working with Tim Snellings above to try to get vimeo embedding in the moodle mobile app (on the public ios app store).
Embedding does work in a mod_label activity with direct embed code but not when using the mod_url activity. So I don't think any of these server settings are relevant since we can get the video to embed.
We have no privacy or domain restrictions on videos and embedding works fine in the browser. Youtube embeds in the app as well but Vimeo doesn't and we get a blank screen. We are using the mod_url activity with a basic https:// vimeo.com/813446759 url and display set to embed.
I've tried with/without the x-frame-options header, have removed it now.
Have enabled the vimeo media player and turned on/off allowframeembedding.
We have a very basic moodle site with almost no plugins and default settings so I'm not sure why this wouldn't work.
Do you know how the app works, is it using a normal iframe embedding method in the mod_url page?
I wonder if you have a test moodle site where you can try embedding that video above in mod_url, does it work in the app for you?
Super grateful for any more tips you can give us!