I depend on FireWire audio interfaces, so everything from Tahoe on is dead to me for the foreseeable future.
My problem is that I don't do audio recording often enough to justify spending the thousands of dollars it would cost to buy all new hardware, but I do it often enough that I can't upgrade my operating system and lose the capability. It's that really annoying middle ground that Apple really doesn't support well, though to be fair, I've gotten thirteen years out of it after Apple stopped shipping built-in FireWire ports, so I guess that's not too horrible. :-)
I tried getting off of FireWire a long time ago, precisely because I suspected that this would eventually happen. But to keep costs down, my plan was to buy a MOTU LP32 ADAT-to-AVB bridge so that I could keep using 16 inputs from my existing interfaces and supplement that with a MOTU Stage-B16. The problem is, the LP32 has been on permanent back-order for about two years now, with no sign of things improving.
I'm also a late adopter after lots of bad experiences, so I just downloaded Sequoia so that at least I won't be stuck on Sonoma forever. I'm hoping that by the time they stop shipping security updates for Sequoia, either MOTU will have the LP32 available again, someone will have figured out a way to get IOFireWireFamily to build and run on later OSes, or I will have found some other low-cost solution for a large number of inputs. Not holding my breath, though, on any of the above.