Opening documents fail because of content security policy violation

That page sure is being referred to an awful lot. Yes I did not explicitly mention that I read that page. The post was getting rather long.
Perhaps not intended but the reply comes across as “I have the answer but I prefer you find out for yourself.”.

Now of course I read the page again cause I am a dumdum It wouldnt be the first time i missed key information. I figure hey perhaps I can make the correct URL stick using the commands described.

That did the same as in the GUI though because the URL is basically the same. (it also shows use build-in-CODE server in the GUI)

Now I did find at least one instance in the page source where it refers to the instance host-name rather than the reverse-proxy host-name.
in https:///index.php/apps/richdocuments/index?fileId=895&requesttoken=&path=%2Ftest_doc.docx
there is
var richdocuments_urlsrc = ‘https:///apps/richdocumentscode/proxy.php?req=/browser/a4b9c74/cool.html?’;
defined.
That one is apparently unaffected by setting the overwritehost value.
The richdocuments app appears to have an issue in it where it doesn’t follow the NextCloud overwritehost value.

For those unaware: You may not load content from another host than the one originally serving the request, doing so will make your browser freak out. (for good reasons though, keeps you safe)