[mst]

See if Ctrl-[ works.

I tend to hit that instead of Esc everywhere I'm using a vi-like after having a weird keyboard issue that nerfed my Esc key for a while (long and uninteresting story) and then finding that Ctrl-[ was more comfortable for me anyway.

(of course that may not work at all in the lambda editor, I'm mostly using it in terminals with heirloom-ex-vi, but seems easy enough to TIAS some time)

[setopt]

Another option worth trying is pressing Ctrl-C. Unlike Ctrl-[, it’s not 100% equivalent to ESC (e.g. it prevents abbreviation expansion), but it does put you in normal mode without losing what you did in insert mode.