It builds the kernel module for your specific kernel. It’s not different from the nvidia package, that’s just the same thing pre-build for the default kernel (in fact if you install both nvidia-dkms will build the module locally, then realize the exact same thing it just build is already there and move on…).
That’s probably the ugly method but as it’s my personal device I didn’t see a problem adding such things to /etc/environment
PS: You should be able to also set this when starting i3 with “QT_QPA_PLATFORMTHEME=qt5ct i3”…