I’ve published Thunderbolt 3 Unblocker, a macOS kernel extension that patches IOThunderboltFamily to disable peripheral compatibility checks. This permits the use of some unsupported peripherals such as the Razer Core external GPU enclosure.
One vendor explained,
Apple has chosen to prevent Thunderbolt 3 devices using currently available controller chips from Texas Instruments from enumerating and functioning on the 2016 MacBook Pros. … Thunderbolt 3 peripherals [released prior to November 2016] which use this controller chip are incompatible with the new 2016 Thunderbolt 3 MacBooks.
These existing devices use Intel’s Thunderbolt 3 chipset (Alpine Ridge) in combination with the first generation of TI USB-C chipset (TPS65982). Apple requires the 2nd generation TPS65983 chipset for peripherals to be compatible.
Of course, patching your kernel to make it do unsupported things is not the most cautious idea, and there is likely a reason why Apple decided to disable this older chipset in the first place.
Previously, Tian Zhang’s TB3 Enabler script could be used to patch the IOThunderboltFamily binary on disk. This technique required that the script be kept in sync with macOS releases. The patch would also need to be reapplied after every system upgrade, and reverting back could be difficult. The runtime patching technique of Thunderbolt 3 Unblocker addresses all of these shortcomings.
One of the contributions of Thunderbolt 3 Unblocker is xnu_override, the small static library that does the patching in the kernel. (A few people also wrote to me to mention Lilu, a larger project with similar goals.) One nice feature of xnu_override is that it can revert all patches when you unload the kext.