Catalina software lifecycle

Nobody here can answer that. Here is how Apple defines Vintage and Obsolete products.

Apple has historically supported the three most current operating systems.

What a third-party developer supports is up to them, not Apple.

Apple is a hardware company, not a software company. They design the OS that they bundle with a Mac to support that Mac that they are selling right now, not the one they sold 10, 7, 5, or even 1 year ago. They optimize their OS for the newest hardware they have installed and usually discard support for older hardware.

Your Mac mini has been able to produce apps for ~seven years, so far.

Apple typically requires the current Xcode release for products released through the Mac App Store, and that version of Xcode works on the current and usually on the penultimate macOS version.

Per current Apple statements on this topic: Starting April, 2020, all apps submitted to the App Store will need to be built with Xcode 11. Xcode 11 requires macOS Mojave 10.14.3 or later.

What will be required with the release of Big Sur, and with the arrival of Arm-based Mac systems, we shall learn.

If you’re not releasing apps through the app store, then you have somewhat more leeway here. With iOS apps though, you’re usually using the App Store.

From the other side of the question and with app usage, typical developer practice for supported target versions is the three most recent releases, and sometimes more.

In terms of running and using the systems, anything past the most recent three versions is headed for more work, and eventually more trouble.

Older than El Capitan right now will be having more trouble making secure network connections, for instance.

I'm not sure what kind of rules you are envisioning.

Developers can support whatever OS version they want to support.

You do need newer versions of Xcode to use new hardware and new OS versions.

App Store requirements are separate issue and covered by MrHoffman.

Since the App Store is the only place you can distribute iOS apps, you would need to meet those requirements. If this is really a question about iOS, then the iOS/iPhone forums might be a better place to ask. The Developer forums might be an even better place.

You don't have to distribute Mac Apps on the App Store, so you can develop for whatever OS you want.

AntonKL wrote:

Oh, so there is no restriction from apple for software developers and operating system versions?

If you’re developing apps for iOS or iPadOS and are distributing through the app store as is typically necessary, then there absolutely are rules and requirements.

I thought there was some kind of rules for that.

For hacking away locally with your own devices and your own systems, no. Have at.

For accessing the developer portal and for tasks such for app notarization, you’ll need to keep your tools fairly current.

For distributing iOS, iPadOS, tvOS, or macOS apps through the Apple App Stores, yes, you’ll need to stay current. There are rules and requirements there.

So... what are your particular app development requirements, and what and what sort of app distribution is planned here?

Are you a member of the Apple Developer program?

As for that other system... OS X 10.6 Snow Leopard was released in 2009. That’s nine versions back. I’m surprised that Snow Leopard was still connecting to websites requiring security. Most stuff prior to OS X 10.11 runs into trouble there. macOS 10.15 Catalina is current. Check the backups configured with that system too, as hard disks that old do tend to degrade and get slower and then fail. Or the old hard disks just fail.

AntonKL wrote:

So... what are your particular app development requirements, and what and what sort of app distribution is planned here?

Are you a member of the Apple Developer program?

Its an app for iphone.

Then you’re going to need to stay current for your purposes, as Apple won’t accept builds from older tools.

Yep, iam member of this program.

Have a look at the iPad and iPhone app submission rules, then. Those are what apply to you and your use of the App Store distributions.

As for that other system... OS X 10.6 Snow Leopard was released in 2009.

Yep, after such experience, i decide that missed new version of software becauseof apple rules.

But it looks like it basically developers of software was responsible.

Arguably, still running Snow Leopard in 2020 was responsible for the effort involved here.

Not many iOS developers still support iOS circa 6, after all. Do you?

The further back computer operating system software and apps get, the larger the effort of upgrading involved, at least until the “just start over again” stage is reached.