Jonny I think a web app would be a great step towards making Cleft Notes available to as many people as possible. Android may take more work because of its fragmentation and abundance of phones with vastly different specs, which is why developing for iOS and MacOS first makes sense.

On the other end, part of the reason I suggested the web app is that most people use a Chromium based browser, which get automatically updated regularly. As for the implementation, Notion comes to mind. I haven't seen the MacOS version, but the web and Windows app are very similar in terms of features, and make the transition from one to another seamless.

Happy to help with testing if able. Let me know!