I recommend contacting developers and telling them about this. You can just copy paste what I wrote to their github account.
[Now possible to add your software as a third party app in the Nextcloud store so people can more easily find it](https://github.com/nextcloud/appstore/issues/95#issuecomment-621959723). Thanks for making this. :heart:

What they see on github is:
Now possible to add your software as a third party app in the Nextcloud store so people can more easily find it. Thanks for making this. 
