Is this macro mapped in vim or OS level? Sounds interesting.

Last time I checked, on all OSes you need to install some third-party software alas. Hopefully I am wrong now.

I configure it in the firmware of my keyboard with QMK

I believe it's done via a daemon that intercepts keystrokes

I have hesitated many times to set this up but I don't want to get used to something that I cannot set up in less than 30 seconds on a new machine.

Not having Escape where CapsLock sits on a new machine already makes it infuriatingly unusable already :)

Which tool can do that kind of wizardry? I've seen either but not both.

On macOS I use Karabiner-Elements to do the exact same thing. Also, my config is only applied in terminals, everywhere else the original functionality is kept. So, I'd say it is quite flexible.

I have similar types of bindings. I just found a keyboard that can use ZMK. There's quite a few out there.

ZMK (or it's free software cousin QMK) are super flexible and you can create lots of custom behaviors for keys (tap/hold behaviors, double press, layering, etc...). It takes some time and effort to learn how to set it all up. Some of the more complicated behaviors require using their dsl for mapping the keys instead of their GUI editor. Considering the ridiculous amount of hours I spend at my computer using a keyboard, I felt it was worth the investment in learning.

Karabiner on macos, keyd on Linux.