I've released the App in the app store. If you are interested, go to the app store and search for calibre connector. It's a free app with no ads.
The support url is
https://www.phillipwwalker.net/
This particular app is a hobby app. I wanted the functionality, so I wrote an app to do it. It has a somewhat different approach than the old calibre companion did. BTW - I PM'ed the creator of Calibre Companion to let him know what I was doing. I really like that app and use it on my kindle fire.
Calibre Connector has some different things, such as syncing, i.e. automatically download any missing books and a reading list. I support the user defined columns in Calibre that I actually use. The app is open source, with the open source URL on the Under the Hood page on the support website.
As can be inferred from this, the app is provided as is. I simply don't have the resources to provide a lot of support. It's been tested on an iPhone, an iPad mini and a iPad Pro.