Nextcloud version (eg, 20.0.5): 23.0.4
Operating system and version (eg, Ubuntu 20.04): debian 10
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.38
PHP version (eg, 7.4): 7.3
The issue you are facing:
Documents created with Nextcloud can be edited if connected but if you send a shared link to some people they cannot edit it … of course link has been set as authorizing edition.
Is this the first time you’ve seen this error? (Y/N): Yes, IIRC it was working with OO
Steps to replicate it:
create a new document (text .odt or spreadsheet .ods)
you can edit it from within NC
create a shared link
send it to somebody that does not have an account or is not signed in … if he tries to edit, NC is proposing download intead of edition
Out of curiosity, have you edited this particular file from a Web Dav set up? (creating a network location on your machine and accessing it from Microsoft Office apps)?
I think this could have something to do with it because I have this same issue and it appears to be intermittent.