Only public health organizations are able to deploy contact tracing apps to the App Store. You'll need to get the relevant department in your country's government to apply for an Apple Developer account which in turn would be used to upload the app.

By now you should just get the M1 Mac Mini.

The concern is that people with less bandwidth would be more hesitant to download your app. iOS devices would download the device-specific version whereas the Mac App Store would download the entire binary (all architecture slices).

Depends on how you distribute your application. If it's an App Store app, you would need to use iAP for almost all digital services (one notable exception is currency exchange or money transfers, only applicable to licensed financial institutions). If it is accessed from the web browser, no need to use iAP. However privately-distributed custom apps also do not need to go through iAP. That is regardless of the technologies used to develop the app.

It sounds like your app may have look-and-feel that is similar to a more established competitor. You might want to review competing apps in the same category or targeting the same audience and see whether any strikes resemblance with your app. Notably the ones that has more downloads (or simply been around much longer than yours). For further information, search the web for "Look-Alike Apps are Considered Spam by App Review" – you should find more pointers on how to tackle this issue.

There are a number of app genres that the App Store reviewers decided to be too saturated. Among those are astrology, horoscope, palm-reading, and similar tell-your-future-from-your-biometric apps. If your app is one of those, you can't publish it on the App Stores. You could try publishing it as a Developer ID macOS application – use Catalyst if it's an iOS app. However there are other causes of "Guideline 4.3 Spam" rejection: Publishing similar apps that differs only in content. Publishing white-label apps under your own Developer Account. A competitor's app looks similar to yours. Search the web for "How to Pass App Store Review: Guideline 4.3 Spam" to find out how to diagnose the problem further as well as some potential solutions.

The problem is that you've submitted a pre-existing app as a new app. That would put a "this account is a spammer" flag on to your developer account. Once that mark is placed, is hard to get it removed. My suggestion would be: Remove the second app (which is stuck at "in-review" anyway). Do a competitor analysis and ensure that your app isn't similar to any pre-existing app nor it is a "saturated" app genre (such as horoscope apps). Update the first app with the new design / code / functionality. In first try, you would likely get rejected anyway regardless of what you uploaded. Then appeal to the App Store review board to get more senior members of the team to review your app. If it's really unique and worthy of the app store, you should get the update approved.

For the record (and now since M1 units are released), Thunderbolt 3 is supported but not eGPU. The M1 SOC does not support external graphics processors as of macOS 11.0. Moreover apparently the corresponding eGPU kernel extensions are present and installed in the operating system partition, but only compiled for Intel.

The biggest hurdle for Data Science on Apple Silicon is gcc (the GNU Compiler Collection). The compiler hasn’t supported Apple’s ARM architecture (instruction set, calling convention, object format, etc) since an ancient version of iOS. Work on that is in progress, but as with all open-source efforts, there is “no timeline” since commitments are done on a “time-available” basis. Lack of GCC implies lack of FORTRAN support. The other notable FORTRAN compiler is Intel’s, and the latter is very unlikely to be ported to Apple Silicon. No FORTRAN also means a lot of numerical libraries are being held back (e.g. SciPy, BLAS, LAPACK, etc). In any case, you could probably run your data science workloads under Rosetta 2 (i.e. Intel emulation/translation). Geekbench has shown that the M1 processors are faster than many Mac portables that came before it, even when running Intel apps. Search the web for “How to Run Legacy Command Line Apps on Apple Silicon” to set up your Terminal sessions to prefer running Intel applications.

Apple hasn’t develop any publicly-available Fortran compiler to date, and there is no indication that would change. Furthermore lack of gcc (the GNU Compiler Collection) support for Apple Silicon seems to be holding back Fortran as well, since many open source Fortran project seems to depend on that. In any case, you could run gcc (and thus Fortran) under Rosetta 2. Many CPU-oriented Benchmarks has shown that the M1 already runs Intel apps faster than most portable Macs that came before it. Search the web for “How to Run Legacy Command Line Apps on Apple Silicon“ to set up a Terminal profile that runs Intel apps by default so that you can continue using Fortran in “Intel mode” until native support finally arrive.

Open-source support for Apple Silicon is mainly held back by GCC’s (the GNU Compiler Collection) lack of support for the architecture. There are work progressing, but as with all open source, that would be in a “time available” basis. Likewise Docker support is progressing, but again there is no timeline. Moreover if you’re depending on x86 Docker images, you would likely need to wait longer for it to provide Intel emulation. Since Rosetta 2 does not support virtualizing x86 systems, Parallels and VMWare would also need to come up with their own emulation software to support running Intel operating systems on Apple Silicon hardware. If you really need to run x86 Docker images, a good alternative would be to buy an Intel Compute stick (a ~$100 USB-powered computer) and install Linux on it. Then you could ssh into the machine to do “Linux stuff” (including testing your server software) and run x86 Docker images. Yet keep most of your tools on the Mac. You could also set up a Terminal profile to run command-line software in “Intel mode” by default. This include gcc and most of Homebrew – until they natively support Apple Silicon. Search the web for “How to Run Legacy Command Line Apps on Apple Silicon“ to get instructions how to do this.

Have you tried appealing to the Review Board? The appeal message could contain / reference the e-mail that you've sent to AppStoreNotices@apple.com (preferably attach copies of the e-mail and resolution reply, if any).

How did it went? FWIW, you could send TestFlight copies to the complainant such that they could approve the resolution of the dispute before sending it for App Review.

Yes you can. Have the watchOS app embedded into the iOS app but only activated when the user has purchased the corresponding iAP from the iOS app. Examples of apps which does this includes Nano and 1Password. Search the web for “How to Sell watchOS Applications as an In-App Purchase” for more information.

What’s preventing you from separating out that user-specific slight difference out from the application bundle? That way you could notarize just one application bundle for all users.