Long time lurker, first time poster.
I thank this wonderful community for all its sharing.
As Monterey no longer offers full support for the older OHCI USB 1.1 standard, quite some users experience that the Bluetooth part of the BCM94360CD WiFi / BT combo module in their classic Mac Pro 4,1/5,1 can no longer function properly when connected in the old way. Some have a flaky/shaky connection, some have no connection at all, some experience a bit of functioning but only at very short distances.
Once we decide to move over to Monterey, we need something in between the old BT-plug on the backplane board and the combo module –or the same module on a Fenvi board– to bring back full functionality. We do this by forcing the system to always make use of (EHCI) USB 2.0, for which there still is support under Monterey.
In case you would like to connect your Fenvi T919 card, an OSX WiFi card or any Chinese combo module to an internal USB connection and have it working under Monterey, without the need for an outside hub and a cable to feed back in, then this may be the all-internal, plug-'n-play solution you're looking for to make Bluetooth 4.0 work properly again under macOS Monterey & later on the Mac Pro 4,1 & 5,1.
Best made in heat-resistant ASA plastic (for up to 105ºC / 221ºF).
Sits neatly behind the CPU cooling block (without touching the cooler) and fits both dual-CPU & single-CPU machines.
Requires no modification whatsoever to the Mac Pro housing, but one does have to temporarily remove the CPU tray.
Offers full functionality, like normal sleep capability, wake-from-sleep by touching a wireless mouse, trackpad or keyboard, Watch Unlock, Handoff, AirDrop, et cetera.
Suited for both 'pure' OpenCore installations and for OCLP installations.
Works 100% fine together with any USB 3.0/3.1/3.2 Gen 1 or 2 PCIe card if present, in contrast to the current OCLP software approach where you can only get BT 4.0 working if you leave out the USB 3 card.
Thoroughly tested during many weeks under real-life circumstances while running various macOS versions, in both MP 4,1>5,1 & 'real' 5,1.
No additional software is required. Connected this way, it's backwards compatible with any flavour of macOS / OSX under which the BCM94360CD can usually function (for 'Handoff' one needs 10.10+) and/or whatever early version of macOS your GPU allows. Also suited for the BCM94360 -CS -CS2 -2CDP (BT 4.2).
Not suited –or needed– for Mac Pro 1,1 / 2,1 / 3,1.
Last but not least: In case you ever invested in a BT 4.0 solution but in practice never got around to using anything else but the basic BT functions towards a keyboard or mouse, you may be well off by activating the Monterey support for the old BT 2.1 module in the OpenCore config (if the little BT 2.1 board and cable are still present). This actually works quite well, especially when adding an external BT antenna. But of course, in that case there's no support for any function that requires BT 4.0 or later.