As of today, the only Intel systems available new via the Apple store are M1 and M2 systems;
Not sure what you mean here. Apple still sells one Intel Mac, the Mac Pro. Otherwise, the iMac still has an M1, the MacBook Air has the lower-end M1 configuration (8CPU/7GPU) as an entry level model, and the Mac Studio still has M1 Max and M1 Ultra. All other Macs are M2 based.
the Intel Mac Mini in particular has now been withdrawn.
Yup. Replaced with the M2 Pro version of the Mac mini.
How long do you folks reckon Apple software and MacOS updates will continue to be developed for my machine? What is likely to be the final OS it will run, when is that likely to be released and when is that likely to become obsolete / unsupported?
This depends on a lot of things. Apple will typically draw this line when introducing a new fundamental system-wide feature that requires hardware support (Metal, in the case of macOS Mojave 10.14.x or HEVC hardware encoding in the case of macOS Ventura). Other times, they'll drop it when they can't update a driver for a given hardware component (as was the reason for 2013 iMacs not getting support for macOS Big Sur when literally every other Haswell based Intel Mac did).
Apple is extremely close to being able to drop support for Intel Macs that lack the T2 Security Chip. With as many features that require either an Apple Silicon Mac or an Intel Mac with the T2 Security Chip, they may simply drop support for Intel Macs that lack the T2 Security Chip. Hard to say. Then again, they could base it off of some hardware feature present in Intel's 8th or 9th Generation Core i3/i5/i7/i9 that drops support for 2017 Macs but otherwise retains support for the 2019 iMacs (which don't have a T2).
The 2018 Mac mini has a T2 and was just discontinued recently, so that bodes rather well for longer term support. Eventually, Apple will stop producing macOS releases that support Intel. But, I'd imagine we still have a bit of a way to go before Apple releases a new version of macOS that won't run on the 2018 Mac mini.
Do keep in mind that, even once a Mac gets to that sad day where it can't run Apple's newest OS, the last OS it can run will still be supported for two years thereafter with security updates and updates to Safari. Most Mac software will, in turn, support the most recent three releases of macOS (provided you are otherwise current with your OS updates). So, when your Mac mini inevitably stops getting major releases, that's not the end. That just means that the two year countdown clock has started.
The standard support should be 5 to 7 years, as long as Apple supports the hardware part.
Apple supporting the hardware with parts isn't necessarily aligned with Apple supporting the product with OS updates. It did seem to happen for macOS Monterey. But that isn't how it's always done.
But of course Apple could cut the support much sooner. That means, that it can happen, that the macOS introduced this year (2023) could be officially the last one, that supports x86/Intel Macs.
Yes, it COULD happen. But this is highly implausible. They know fully well that there've been people buying Intel Macs for the last 18 months (and higher end ones at that) who would be pissed. I'd say the worst they'd do is cut support for non-T2 Intel Macs, pissing off the 2019 iMac crowd. But wholesale? Nah, we're still a few releases away from that sad day.
They are likely to force users to switch as quickly as possible to Apple Silicon (ARM).
Let's wait and see...
They want people to buy new Macs. But they don't want people who bought $2000-50000 Macs to be left out in the cold THIS soon because they know they'll have customers leave them. They'll probably be supporting the 2019 Mac Pro for a long while. Similarly, the iMac Pro is a tank the way that all Xeon computers are tanks.
