Joplin was relatively simple to setup on NextCloud. The only difficulty is setting the folder it should run out of. This is done via the webdav url that Joplin connects to. An example is shown below on how to get this going.
/<username>/<path to Joplin directory>
The webdav url just needs your username and the path it should utilize, in my case I just have Joplin setup to go to Documents/Joplin. This would go in the tag above, just add a username and it’s done. This does have to be setup the same way on all Joplin clients or you will end up with files missing from one or another, though they will all be in NextCloud.