I'm wondering if the issues we're seeing with Thunderbolt 4 hot plug on some of the Z590 motherboards is actually an incompatibility (or bug) with the Maple Ridge NVM 26.x firmware and older Thunderbolt 3 devices? None of my Thunderbolt 3 devices hot plug on the Z590 Vision D, whether in macOS, Windows, or Linux. Someone also told me that upon updating the Asus Hero XIII to BIOS 0704, it updated the Thunderbolt firmware to version 26 (they are not sure what the firmware version was before), and upon updating they're having trouble with hot plugging Thunderbolt 3 devices (hotplug worked fine before the BIOS update).
On the Z590 Vision D, if I plug in a Thunderbolt 3 device, they power on, but they do not appear to receive Pcie lanes, and do not start up, even though the Windows Thunderbolt Control Center says the device is 'connected.' The device appears to connect, but is in a zombie state, it is on, but functionally dead. What I've found out is that in Windows and Linux, if I put the system to sleep after hot plugging a Thunderbolt 3 device, when the system wakes up, the OS drivers appear to reset the Thunderbolt controller, and the formerly zombie devices (that were hot plugged but went into a non-functional state) briefly go off and then come back on, and are recognized by the system. I tried a Thunderbolt 3 dock that wasn't recognizing USB devices after hot plugging the dock. I also tried connecting a Thunderbolt 4 dock, and low and behold, it hot plugs, and attached USB devices connect and are recognized by the system.
So it appears that Maple Ridge hot plug works with Thunderbolt 4 devices, but is currently (as of firmware NVM 26.x) having issues with hot plugging Thunderbolt 3 devices.
What has Intel unleashed ????