The build for this new version of libinput fails due to it wanting a newer inputproto:

 checking for INPUTPROTO24... no
configure: error: Package requirements (inputproto >= 2.3.99.1) were not met:Package dependency requirement 'inputproto >= 2.3.99.1' could not be satisfied.
Package 'inputproto' has version '2.3.2', required version is '>= 2.3.99.1'

x11-proto/inputproto could be updated – this ebuild is actually autogenerated by kit-fixups/core-gl-kit/curated/x11-base/xorg-proto and is a stub ebuild, designed to advertise the level of inputproto support that is bundled into xorg-proto. So this is pointing to a need to update x11-base/xorg-proto... or temporarily hold back on the inputproto update.