I scrimmaged around on the internet and found a third-party place that contains links to obtain the actual latest download directly.
The official Apple methods fail.
- App Store won't let me download it (current Mac too old).
- App store 'Copy link' just redirects me to the App store if I paste it in the browser.
- The InstallAssistant.pkg link supplied by @AlWeir (thank you!) sadly fails after a few MBs have begun downloading. No idea why.
All I needed was somewhere to get the direct download, irrespective of whether my current Mac supports it or not. All this stuff about "I've never had to clean install in 18 years, you should use software update, yahde yahde" is all brilliant in theory, but fails to take into account some people's situations.
I have only one fully-working, ancient 2012-era MacBook Pro running Catalina, and have acquired a newer model (albeit one with the irritating T2 chip/TouchBar but beggars can't be choosers) that was decreed a write-off by the genius bar techs. I stripped it down to bare metal, cleaned it up, hacked off a shoddily-placed capacitor on the logic board that was destroyed by dust build up, put it all back together and the thing miraculously came to life.
But of course, the previous owner who took the Apple-recommended route of buying a new one, had everything locked down. The only thing I appear able to do is CMD-R boot and erase. Hence I'd like to provision Sequoia onto a USB stick installer from this ageing MBP, so I can start afresh on the newer machine, and a direct download to the installer plus running the terminal command to provision the stick seems the only viable route.
When I get round to rebuilding it, there's a slim chance I'll be given the option to reinstall whatever OS was shipped with the machine (assuming the NAND recovery partition is intact) and I may therefore be able to go through the official Software Update route once it's repaved. But if there's any way to start with a clean slate, I'll take it. I don't know if a direct upgrade jump from whatever that version might be (Sierra? High Sierra??) to Sequoia is even possible.
The 15.3GB(!) install assistant is downloading now. Fingers crossed it works...
[Edited by Moderator]