Some time ago I was forced to upgrade to Sierra, because LinkedIn's website stopped working in Chrome. (I don't use LinkedIn much because it's awful, but a lot of clients find me there.) Turns out LinkedIn felt my version of Chrome was too old to support. But why was Chrome too old? Doesn't it update automatically? Yes, as long as the new version supports your OS, and apparently Chrome had stopped supporting Lion quite some time before. So I had to upgrade, and although I would have preferred to upgrade to Maverick, Apple only offered the option to upgrade to the latest version: Sierra.
If Mojave is such a no-go, upgrading to the version just before Mojave may not be possible, so I might be stuck on Sierra until my Macbook collapses, slowly watching websites drop support.
Obviously my next machine is not going to be Apple. I'm probably going to get a ThinkPad with some version of Linux if I can find a nice one.