You can try TeXmacs in your browser at https://yufeng-shen.github.io/Mogan.html . (It's actually from a fork of TeXmacs called Mogan, of which I've been a happy user due to better CJK support.)

By the way, I do think TeXmacs is an Emacsen as it provides Guile/Scheme as an extension language, though I don't know how customizable it is. (I think the built-in REPLs for Python/Maxima/Scheme/... are written in Scheme.) And then, it does support quite some TeX commands (and you input them by pressing backslash followed by their command name), so I do think their "TeXmacs" name is very much justified.

Unfortunately, many Qwerty typing guides group keys in left-leaning columns [1], requiring many to twist their left wrist. And this is why I hope the angle mod [2] from the Colemak community gets more mainstream recognition: instead of learning to twist your wrist, just shift the keys to let them adapt to you. This "un-kinks" the layout, allowing your left wrist to remain perfectly straight while your arm approaches the keyboard at a natural, relaxed angle like the person in the right side of the drawing.

[1] https://www.keybr.com/

[2] https://colemakmods.github.io/ergonomic-mods/angle.html