Nextcloud sharing is quite easy and writing in local editors as Typora or Zettlr is practical. These editors allow different image path settings, many of them are interpreted correctly in Nextcloud, such as Typora’s assets Folder. Now sharing such a markdown file will not transmit it’s image files. It will show an placeholder icon with image name and path.
Only nextclouds own image system, a invisible folder with cryptic numbering like .attachments.111292 will show images of a shared markdown file. This folder will also follow the container file if this is moved to another location in NextCloud.
The use of this system requires creation of such a folder in Netclud, later any editor’s images can be placed in that folder. A bit complicated but manageable.