It's 100% an issue with the software not being implemented correctly for the beta as is clear in the error code; I have that much knowledge of appkit but unfortunately my knowledge stops at being able to fix it (and messing about with it would probably violate SI TOS anyway). Therefore the onus is on the devs to fix it; obviously they're not obligated to do this as it's unsupported software, I totally understand that. But I doubt it would be too difficult to do (devs, if you're reading, feel free to put me in my place if I'm wrong).
The Mac OS 14 Sonoma Public Beta is now available as of 2 days ago, meaning a very large percentage of Mac users will be upgrading or have already done so. The vast majority of these users will have no idea how to downgrade once they realise FM isn't working as Apple intentionally makes this difficult. It's in everyone's best interest to get this sorted.