Having a global keybind to disown the foreground process is impossible: Keystrokes are received by the foreground process, not by the shell. You need to first suspend it with Ctrl+z if you want to disown it.
However, turns out there’s a zsh option to speed up disowning then continuing: With setopt AUTO_CONTINUE, disown will automatically also send SIGCONT.
Sounds like you want termux
Heres a good response on SO: https://unix.stackexchange.com/questions/223432/in-zsh-how-can-i-more-quickly-disown-the-foreground-process/223433#223433