Maybe your distro patches it, but last I checked typeahead wasn't available in GTK-file-picker. It uses recursive search instead.

https://gitlab.gnome.org/GNOME/gtk/-/issues/839

Also: https://bugzilla.gnome.org/show_bug.cgi?id=748672

The GTK devs were saying that they wanted a flag shared between nautilus and the file picker that would enable/disable typeahead. Unfortunately nautilus refuses to implement that flag, which I think means we're all still relying on forks for that feature.

So you're not really allowed to solve one without solving the other, last I checked.

So yeah, the issues is very much in both, and you can't solve the issue with GTK without solving it in Gnome.