macOS allows third-party drivers too, Apple just wants vendors to write them in userspace rather than kernelspace. That’s probably not the worst thing, because proprietary driver code is notoriously shoddy and should be run somewhere that limits the blast radius.
That’s mainly restricted to graphics cards. Audio cards like used for production as well as I/O (USB, etc) and networking cards have drivers and work fine given you have a PCI-E slot to plug them into, and of course almost anything external connected via USB or Thunderbolt works fine. For GPUs, it’s only a specific subset of users that needs a discrete GPU, especially as the GPU built into M-series SoCs has become powerful enough for most uses outside of high-end gaming.
