Looks like this might be coming down the pipe.
I wonder if the proposed command is correct, as
--overwrite was supposed to not have a leading slash for root directory.
pacman -Syu --overwrite=/usr/lib/libnv_vulkan_wrapper.so.1,/usr/lib/libprimus_vk.so.1
pacman -Syu --overwrite usr/lib/libnv_vulkan_wrapper.so.1,usr/lib/libprimus_vk.so.1
The brave guys in unstable will confirm and inform us (to advance our knowledge... )
I just tested this with another package and provoked an existing-file-conflict: both commands have the same result and do overwrite the conflicting file.
It worked fine yesterday morning when I updated. It's good to read the Arch homepage prior to any updating (in Arch). Avoids surprises.