I’m not seeing such a problem on any of my VMs.
This leads to partial update situation (unsupported), let’s hope it doesn’t come to that. If a downgrade is to be attempted however, there are several packages to downgrade in unison…
None of my VMs has xf86-input-vmmouse installed. If you’re using QEMU you should not need it (as it’s a VMWare mouse driver).
I’d remove it.
$ sudo pacman -Rns xf86-input-vmmouse