Man pages matching name io::handle::prototype::fallback in section 3pm:

IO::Handle::Prototype::Fallback.3pm.en	debian 10 / libio-handle-util-perl
IO::Handle::Prototype::Fallback.3pm.en	debian 11 / libio-handle-util-perl
IO::Handle::Prototype::Fallback.3pm.en	debian 12 / libio-handle-util-perl