Why has the term "microcomputing" been used less and less since 1986-87 (ngram)?
What term has replaced the term "microcomputing" since 1986?
In the early days of computers, computers were huge machines that filled gymnasium-sized rooms. Over time, they got smaller until a market segment of computers that could sit on a desk appeared. Those computers were called microcomputers.
Eventually, all computers were miniaturized to the same scale; "mainframe" computers were just slightly bigger, more expensive micros. There was no longer a need to distinguish between microcomputers and any other kind of computer so the micro- prefix disappeared.
As for what "replaced" it, the various other computer terms have replaced it. Microcomputing is just computing with a computer.