I am posting these thoughts some time after your issues, but I have just been through the same thing and think its worth putting this up.
After upgrading the computer in my studio I put a FireWire card in a new Windows 11 machine and sudenly nothing worked. Turns out that only certain TI chipsets will play nicely with Windows 11 and FireWire and that Windows 11 does not consider FireWire a relevant issue. Support is only there because of legacy drivers and a bit of good luck. Feels a bit shit to loose legacy support for such an important part of our industry but the latest USB specifications and Thunderbolt have sent FireWire to the "Betamax" heap.
After a lot of reading in many places there were a few messages of hope and before I set about downgrading the operating system to windows 10 in the hopes of making my FF800 work, I decided to try more than one FIreWire card - and the one maufactured by Syba worked. Good luck.
This Syba low profile card has a TI XIO2213 chipset and it worked for me.
https://www.amazon.co.uk/Syba-Profile-P … B002S53IG8
This is the one I had first and it most certainly did not work (Here is a link anyways)
StarTech.com 2 Port PCI Express FireWire Card - 1394a Firewire - TI TSB82AA2 Chipset - Windows & Mac Compatible
https://www.amazon.co.uk/gp/product/B08 … prod_image