I think I’ve managed to achieve what you want, but it took takes a lot of work. My solution is definitely not for everyone, and probably not even for 90% of Linux users.
I’ve been using the same install of my operating system for 25+ years, and the same desktop environment for probably 20. Except, everything is also the newest version with all of the latest security and feature updates.
My laptop has an install of Debian Sid/unstable, which I first installed around 1998. Whenever I get a new laptop, I just copy it from my old one over to the new one, make whatever tweaks are necessary to use the new hardware, and get back to work. Sid is a rolling release, so as the various programs that make up Debian are updated, my laptop updates.
My desktop environment is based on Xfce4, which has been out since 2003, though I don’ think I’ve been using it that long. Occasionally there is an update which breaks some widget I’m using, but the parts I interact with essentially stay the same.
It takes work to keep all of that the same. It would be easier to just update to whatever the newest Ubuntu is, and then every 6 or 12 months, upgrade again, and take the hit if something major changes.
Microsoft could run a similar process. Keep the Windows 7 interface with a few changes to take advantage of new hardware abilities, and upgrade the guts with new features and fixes, but from the outside it would look very much the same. Old hardware would occasionally lose support, and some new features might only be available on new hardware.
I think that was even Microsoft’s plan with their Windows 10 forever idea, which didn’t last.