Some PCs just last. A 2.4 GHz Core2 Quad I had, I think from 2008, is still going strong and can run most modern software just fine.
It's amazing how little progress there has been in last 13 years. In the nineties you had to upgrade every two years or so just to be able to run current software.
I think 2021 computer has a good chance of being still completely usable in 2040.
I'm currently building my next computer, and the difference again is just staggering. And that is not even factoring in that the next one has got 12-cores.
It is not that the progress hasn't been slow (I guess it has if you compare it to the pace of the past), but I think it has more to do with computers back then still being very capable.
You can still fire up some CAD software and do proper work on the Q6600. I mean, right until you want to listen to music or do some very light web browsing. Then it will suddenly become quite painful. The amount of waste in today is incomprehensible. No seriously, properly incomprehensible.
I recently set-up my old Q6600 as a station for CNC machinery, that thing flies with LinuxCNC on a small SSD. There's no issue running firefox and a music player at the same time (though I tend to not have other things running when milling something but more by cargo-cult than actual tests of the impact on the real-time behaviour needed for the CNC machine control). Some operations on Inkscape are of course slower than on more recent hardware but otherwise it's still very useable.
And of course you can surf the web. But even with 5GHz turbo it is still slower than a fast connection was in the late 90s (on 90s hardware and browser). And it has nothing to do with that progress hasn't advanced in that time (we are talking orders of magnitude).
Absolute garbage, and entirely representative of all other consumer class software.
I do think I could still manage on Q6600 with 16 GB RAM and an SSD. Might need to downscale VMs and browser tabs, but manageable in a pinch. Heck, in the early nineties I was happy to have an Amiga with 1 MB of RAM and that thing flew in comparison to C64. :-)