NVIDIA 440.44 - Kernel 5.4 PRIME (Compat)
There's a new version out, 440.59, that has native support for both 5.5 and PRIME for >= 5.4.
This one shouldn't break older kernels. Otherwise, nothing should have changed.
A rebased version for 430.xx is available at: https://gitlab.com/snippets/1929571
The latest version, 440.48.02, of the Vulkan beta driver has native support for PRIME Synchronisation.