Manjaro breaks after failed system update

Never do this - quote from Arch Linux Wiki but is equally valid on Manjaro Linux

Warning: When installing packages in Arch, avoid refreshing the package list without upgrading the system (for example, when a package is no longer found in the official repositories). In practice, do not run pacman -Sy package_name instead of pacman -Syu package_name, as this could lead to dependency issues. See System maintenance#Partial upgrades are unsupported and BBS#89328.

pacman - ArchWiki

Always use the following - no matter if it is update or addition (it is always a sync)

pacman -Syu

After successful completion of the system sync (you may need to restart the system)

pamac update --aur

With every announced update to stable the following notice is included

Additional Info

Info about AUR packages

:warning: AUR (Arch User Repository) packages are neither supported by Arch nor Manjaro. Posts about them in Announcements topics are off-topic and will be flagged, moved or removed without warning.