It means "until the third-party developers in the OS's application ecosystem have changed their definition of 'state of the art' to include the use of enough new layers of bloat that old devices can no longer run the newest [versions of] apps."

An obsolete laptop is the same as an obsolete phone: it's one where it chugs when opening Spotify, or Slack, or any other "nobody ever bothered to optimize this" app that everyone uses anyway.

Or, to put that another way: you can certainly retouch photos in GIMP, or even in Paint Shop Pro 7 on Windows XP. But what if you want to use seam-carving in your photo-retouching? PSP7 ain't got that. Once you know that your use-case dictates a modern version of some memory-hogging software, well, that constraint dictates what kind of computer is "obsolete" or not for you.