Apple announced that macOS 10.15 ("Catalina") was available. However, our Post Mojave-compatible upgrade of TopXNotes 2 is a massive rewrite. We are working to deliver this rewrite and will provide more details on our expected delivery date when we have them. Until then, we strongly advise you to delay upgrading from Mojave. TopXNotes 2 will not run on the Apple Catalina or later operating system . We appreciate your patience and apologize for the inconvenience. You must not upgrade to Catalina until we have released the new version. Please check back to this page for updates. We will also send an email (to your email address on file) when we have a definitive release date. We know how important this is to your business and your life. We will do everything in our power to get this done. Thank you for your patience.
If you installed any of the beta versions of the new macOS after Mojave it will be the same, TopXNotes 2 will not be able to run. If you are intending to run TopXNotes 2 on your Mac, do not install the public or developer preview/betas of the new 64-bit operating system.
When running TopXNotes or TopXNotes 2 on High Sierra, MacOS 10.13 (or later) you may see a message about TopXNotes not being optimized for your Mac because it is a 32-bit application. As Apple says in the article linked to the message "Yes, you may continue to use 32-bit apps with your Mac today. Using 32-bit software has no adverse effects on your data or your computer.
You can read Apple's statement on the transition to 64-bit here in this article.