It depends. Some things are visibly awkward, unpleasant to learn and use, and clearly short-lived. It only pays to learn and work on them if you are paid a lot of money. My pet example from the 1990s is Win16, which I skipped entirely for Win32. Many 4GL languages from the 90s stayed there too. Every second of time dedicated to Javascript frameworks before React/Vue was probably a waste of time. (OTOH learning the bare-metal JS paid off well.)