They don’t.

I’m guessing you navigated to the https://mise.jdx.dev/environments.html page and saw the TOML syntax (which looks an awful lot like INI), and confused yourself.

Mise (like a lot of software) uses TOML as the format for its config files (as opposed to something like JSON). Mise reads that config, to automatically export environment variables on a per directory tree basis.

When the docs refer to environment variables, they very literally do mean environment variables. The values of which are taken from a format that resembles INI, as you have noticed.