I don't think it disappears - the copy I have will still be on my machine, and free to use as well. Unless they implemented something to remotely delete it?

Unless you freeze your machine in its current state, software that isn't maintained will eventually stop working.

This is only true for very badly written software, and/or on platforms that maintain very bad backward compatibility. It's not some natural law of software--it's choices that (IMO) bad developers choose to make over and over.

It’s not just the case of badly written software. It will work until they shut off the license servers.

Adobe CS2 is a highly-capable software suite that would happily run on today’s computers. I remember when Adobe shut down the license servers for CS2. They released a version that you didn’t need to activate to assure people that they would still be able to use the software they bought in the future. But then they got tired of hosting the download servers, so they stopped, and that was it.

This already happened with Affinity Photo v1 on iOS; a lot of functionality did not work after an iOS update. It feels like Apple changed something in their libraries, so it doesn't even matter how robust your software is if the underlying OS doesn't honor compatibility.

ok, but if you depend on software for work or business, you do not update your OS until you can guarantee and verify that your software will work.

The original iOS version worked. Maybe don't update iOS if you want to continue using affinity's software?

The Apple ecosystem, in general, is notorious for this: If you update your OS, some 3rd party applications will suddenly no longer work, because Apple keeps introducing breaking changes. But, if you don't update your software, other 3rd party applications will quickly abandon you and block you from using their software until you update. So, you're damned if you do, and damned if you don't. Complicating this is: if your hardware is "too old" (as deemed by Apple), you can't update your software, so eventually you're left in the dust. You can't win.

Unfortunately there's also security people who work day and night to break old software and hardware that cannot keep up with the latest security standards.

This is how things have worked since programmable software was invented.

And proton and the community do well to keep old things working.

Dosbox is a testament to that.

Legally, you can't redistribute it

your gripe is valid but misdirected. I also own a copy but, the one-time validation requires a validation server. Once that server goes offline, i can no longer install Affinity on a new machine.