Man pages matching name sane-st400 in section 5:

sane-st400.5.en	debian 10 / libsane-common
sane-st400.5.en	debian 11 / libsane-common
sane-st400.5.en	debian 12 / libsane-common
sane-st400.5.de	debian 12 / manpages-de