Debian also has libexec. I can see 80 packages¹ in Debian which has files in either /usr/libexec or /usr/$ARCH/libexec. The Debian Policy² does not mention libexec, but does refer to the FHS, which does allow libexec³.

1. Here is the list:

https://tracker.debian.org/pkg/apper
https://tracker.debian.org/pkg/arctica-greeter
https://tracker.debian.org/pkg/arctica-greeter-guest-session
https://tracker.debian.org/pkg/at-spi2-core
https://tracker.debian.org/pkg/bacula-common
https://tracker.debian.org/pkg/dillo
https://tracker.debian.org/pkg/drkonqi
https://tracker.debian.org/pkg/eximon4
https://tracker.debian.org/pkg/fgetty
https://tracker.debian.org/pkg/flatpak
https://tracker.debian.org/pkg/flatpak-builder-tests
https://tracker.debian.org/pkg/flatpak-tests
https://tracker.debian.org/pkg/flatpak-xdg-utils
https://tracker.debian.org/pkg/flatpak-xdg-utils-tests
https://tracker.debian.org/pkg/font-viewer
https://tracker.debian.org/pkg/frameworkintegration
https://tracker.debian.org/pkg/gamemode-daemon
https://tracker.debian.org/pkg/gstreamer-qapt
https://tracker.debian.org/pkg/gtk-3-examples
https://tracker.debian.org/pkg/hotspot
https://tracker.debian.org/pkg/iwd
https://tracker.debian.org/pkg/kde-cli-tools
https://tracker.debian.org/pkg/kde-config-gtk-style
https://tracker.debian.org/pkg/kde-config-gtk-style-preview
https://tracker.debian.org/pkg/kde-config-systemd
https://tracker.debian.org/pkg/kdeconnect
https://tracker.debian.org/pkg/kde-telepathy-auth-handler
https://tracker.debian.org/pkg/kde-telepathy-call-ui
https://tracker.debian.org/pkg/kde-telepathy-filetransfer-handler
https://tracker.debian.org/pkg/kde-telepathy-text-ui
https://tracker.debian.org/pkg/khelpcenter
https://tracker.debian.org/pkg/kinit
https://tracker.debian.org/pkg/kio
https://tracker.debian.org/pkg/kwin-common
https://tracker.debian.org/pkg/lambda-align2
https://tracker.debian.org/pkg/libexecline2.5
https://tracker.debian.org/pkg/libexecline-dev
https://tracker.debian.org/pkg/libexecs0
https://tracker.debian.org/pkg/libexecs-dev
https://tracker.debian.org/pkg/libexecs-embedded0
https://tracker.debian.org/pkg/libkf5config-bin
https://tracker.debian.org/pkg/libkf5kdelibs4support5-bin
https://tracker.debian.org/pkg/libkf5purpose-bin
https://tracker.debian.org/pkg/libkf5screen-bin
https://tracker.debian.org/pkg/libkf5su-bin
https://tracker.debian.org/pkg/libkf5wayland-dev
https://tracker.debian.org/pkg/libkf5xmlgui-bin
https://tracker.debian.org/pkg/libkim-api-dev
https://tracker.debian.org/pkg/libkscreenlocker5
https://tracker.debian.org/pkg/libktpotr9
https://tracker.debian.org/pkg/libmbim-proxy
https://tracker.debian.org/pkg/libmodsecurity3
https://tracker.debian.org/pkg/libqmi-proxy
https://tracker.debian.org/pkg/mlucas
https://tracker.debian.org/pkg/ntpsec
https://tracker.debian.org/pkg/openconnect
https://tracker.debian.org/pkg/opensmtpd
https://tracker.debian.org/pkg/opensmtpd-extras
https://tracker.debian.org/pkg/os-autoinst
https://tracker.debian.org/pkg/ostree-boot
https://tracker.debian.org/pkg/ostree-tests
https://tracker.debian.org/pkg/plasma-desktop
https://tracker.debian.org/pkg/plasma-discover
https://tracker.debian.org/pkg/plasma-discover-backend-snap
https://tracker.debian.org/pkg/plasma-workspace
https://tracker.debian.org/pkg/plasma-workspace-wayland
https://tracker.debian.org/pkg/polkit-kde-agent-1
https://tracker.debian.org/pkg/powerdevil
https://tracker.debian.org/pkg/pulseaudio-module-gsettings
https://tracker.debian.org/pkg/remote-logon-service
https://tracker.debian.org/pkg/rkward
https://tracker.debian.org/pkg/seahorse
https://tracker.debian.org/pkg/sysprof
https://tracker.debian.org/pkg/tomcat9
https://tracker.debian.org/pkg/tomcat9-common
https://tracker.debian.org/pkg/xdg-dbus-proxy-tests
https://tracker.debian.org/pkg/xdg-desktop-portal
https://tracker.debian.org/pkg/xdg-desktop-portal-gtk
https://tracker.debian.org/pkg/xdg-desktop-portal-kde
https://tracker.debian.org/pkg/xdg-desktop-portal-tests

2. https://www.debian.org/doc/debian-policy/

3. https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html#us...