Thanks, Martin.
PACE emailed us late last night to say that they're investigating with Apple, and that Apple is planning to fix it in an upcoming update (schedule unknown as yet). Based on their description, I think it probably wouldn't affect Hauptwerk, since, so far, they think it's specific to iLok-protected native-ARM AU plug-ins, and Hauptwerk's AU plug-in (the "Hauptwerk AU Plug-in Link") isn't itself iLok protected, and also it runs under Rosetta. Hence hopefully it won't affect us, but it may be advisable to wait until avoid installing macOS 14.4 anyway (and especially so if one uses any other AU plug-ins) until there is proper fix for it from Apple or a work-around from PACE.