sudo pacman -Syu was most likely a typo, thanks!
In fact this was also conducted: pacman-mirrors --fasttrack && sudo pacman -Syu.
Reinstalling pamac leads to error, too:
[manjaro /]# pacman -Syu pamac
:: Synchronizing package databases...
core is up to date
extra is up to date
community is up to date
multilib is up to date
warning: pamac-gtk-11.7.2-0 is up to date -- reinstalling
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...
Packages (1) pamac-gtk-11.7.2-0
Total Installed Size: 0.53 MiB
:: Proceed with installation? [Y/n] Y
(1/1) checking keys in keyring [####################################] 100%
(1/1) checking package integrity [####################################] 100%
(1/1) loading package files [####################################] 100%
(1/1) checking for file conflicts [####################################] 100%
error: failed to commit transaction (conflicting files)
pamac-gtk: /etc/xdg/autostart/pamac-tray-budgie.desktop exists in filesystem
pamac-gtk: /etc/xdg/autostart/pamac-tray.desktop exists in filesystem
pamac-gtk: /usr/bin/pamac-installer exists in filesystem
pamac-gtk: /usr/bin/pamac-manager exists in filesystem
pamac-gtk: /usr/bin/pamac-tray exists in filesystem
pamac-gtk: /usr/lib/libpamac-gtk.so exists in filesystem
pamac-gtk: /usr/share/applications/org.manjaro.pamac.manager.desktop exists in filesystem
pamac-gtk: /usr/share/applications/pamac-installer.desktop exists in filesystem
pamac-gtk: /usr/share/dbus-1/services/org.manjaro.pamac.manager.service exists in filesystem
pamac-gtk: /usr/share/gnome-shell/extensions/pamac-updates@manjaro.org/README.md exists in filesystem
pamac-gtk: /usr/share/gnome-shell/extensions/pamac-updates@manjaro.org/extension.js exists in filesystem
pamac-gtk: /usr/share/gnome-shell/extensions/pamac-updates@manjaro.org/metadata.json exists in filesystem
pamac-gtk: /usr/share/gnome-shell/extensions/pamac-updates@manjaro.org/stylesheet.css exists in filesystem
pamac-gtk: /usr/share/gnome-shell/search-providers/org.manjaro.pamac.manager.search-provider.ini exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/16x16/apps/system-software-install.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/32x32/apps/system-software-install.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/48x48/apps/system-software-install.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/actions/view-sidebar-end-symbolic.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/actions/view-sidebar-start-symbolic.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/emblems/globe-symbolic.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/installed-check.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/pamac-tray-no-update.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/pamac-tray-update.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/software-install-symbolic.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/software-remove-symbolic.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/software-select-symbolic.svg exists in filesystem
pamac-gtk: /usr/share/icons/hicolor/scalable/status/software-update-symbolic.svg exists in filesystem
Errors occurred, no packages were upgraded.
Command
inxi --admin --verbosity=8 --filter --no-host --width gives no output (within chroot).
I should probably add the information that I chrooted manually, following this excellent guide ([HowTo] Chroot from or into any Linux distribution), instead of using manjaro-chroot -a (since my drives are encrypted).