In both of the following cases,
printf 'getpin\n' | pinentry-gnome3 --no-global-grab
printf 'option no-grab\ngetpin\n' | pinentry-gnome3
I personally prefer system-modal interaction with the pinentry, but it seems like the documentation and status feedback should at least match the behavior. it currently does not, as the documentation implies at least that --no-global-grab should indeed work, and pinentry-gnome3 returns OK when the user sends OPTION no-grab.
I ran into this while triaging https://bugs.debian.org/930062