What is the opening value of 1. e4 in 2020? Bobby Fischer:


  e4 -- best by test.


What is the current theory or trend in theory behind this statement?

We have seen huge strides taken in chess AI in the past two years. How is this affecting opening theory regarding the "best first move"?
It's still one of the best moves White can play. There's no clear consensus on whether 1.e4 or 1.d4 is better, but it's played frequently at the top level. Due to advancements in theory, I'd say 1.e4 isn't regarded quite as highly as it was in the past, but again it's most likely White's best/second best move.

Advancements in AI aren't really affecting theory on the first move. Games from AlphaZero/Leela are good for new ways of thinking in the middlegame or late opening, but they're not changing our fundamental opening understanding.

EDIT - also, technically 1.e4 isn't "best by test" currently. In my database it scores 52.8%, while 1.d4 scores 54.4%. But to be fair, 1.e4 has been played in roughly 1.5 million more games, and the types of players who favour 1.e4/1.d4 may differ.