I use a 3rd party repo for ZFS drivers, which gets checked for compatibility with each new kernel release by the maintainers, so ZFS frequently stops me from upgrading, and crucially it stops me after I've already fetched the new package databases.

Running pacman -Sy and then installing an individual package isn't supported and it's understandable why.

Running pacman -Syu and having it break sticks you into this limbo where if you install anything before finishing the upgrade, you risk shooting yourself in the foot.