ALAN. Avoid Learning Anything New Terrible advice and mindset, It's good to learn for pleasure or curiosity. This way, you can enjoy reading SICP, effective java, code complete... Or you can use a new system, Linux, Mac, Android, iOS. Doing it you model your thoughts and mind, learn new ways, practices, or patterns, you don’t have to use then only for having learned, but even so, they will be useful to you.
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 ba…
Also, having spent time on frameworks before React/Vue makes you really appreciate what React/Vue do for you.