The terminal is emulated into a Vim buffer which means that you can treat it
sort of like any other Vim buffer. You start in Normal mode. Once you use
any mapping that would transition you into Insert mode, you’ll instead find
yourself in Terminal mode. Terminal mode works just like any
ls a try).
<Esc> though and you’ll see that you stay in Terminal mode
instead of being transitioned back to Normal mode.
So how do you get back to Normal mode?
This is a pretty awkward key mapping though, so follow the Nvim Terminal docs and bring back the Escape key.
:tnoremap <Esc> <C-\><C-n>