I don't think this is realistically true in the age of cloud services and forced, automatic updates.
Maybe it is if you painstakingly stick to decades-old software or FOSS - but this will mean you're missing out on a lot of progress made in modern software.
(edit:)
> ...and probably still have people with modern Flash installations be able to play it back?
Even if you got Flash running on your old PC, this is where things would break. Browsers deliberately increase the friction and technical expertise needed to enable Flash content, with the openly stated goal to drop Flash support completely in the mid-to-near future.
Learning Flash might still be a fun experience if you can keep it on the PC it's produced - but if you want your kid to pass their movies on to anyone else, Flash is nowadays a dead-end.
I agree though with the Doom thing. My suspicion is that in 20 years, many of today's games will be forgotten but people will likely still play FFIV on emulator - not because some artistic quality were better but simply because you can.