welcome to another stable update of Manjaro. We added the latest KDE, renewed most of our kernels and some browsers plus added the latest Vulkan stack. Additionally we added regular upstream updates as usual.
Seems the new libinput update created some issues with some touchpads. If our new kernel updates don't solve the issue for you, you may think about downgrading libinput instead, until upstream found a proper solution for you:
Make sure global menu widget is removed from the Titlebar, for some reason it was added in 5.12 when the global menu setting option was removed.
KDE remove green separator line between Titlebar and Window
System Settings>Application Style>Window Decorations>Breeze>Settings Icon
Turn off “Draw separator …”
On KDE my external drives don't get automounted when I plugged them in
As a workaround put into the KDE/Plasma autostart the program udiskie (just plain like that), after you had installed it. A re-login may be needed to get it active. As alternative start it manually for your current session.
My system won't boot anymore after this update
Most likely you are using a freetype2 package from the AUR. Due the harfbuzz update, your system is broken. So either install the official supported freetype2 package from our repositories or downgrade to harfbuzz v1.7.4: sudo pacman -U https://archive.archlinux.org/packages/h/harfbuzz/harfbuzz-1.7.4-1-x86_64.pkg.tar.xz
updates went fine on my machines, I also grabbed the updated intel-microcode from the link you kindly posted in the other thread @philm and that's also working fine to for my i3-3110m powered notebook.