Some corrections (that I unfortunately cannot edit into my original post!) NSRunningApplication.activateWithOptions isn't deprecated, but the option NSApplicationActivateIgnoringOtherApps is. Instead of NSRunningApplication.yieldActivationToApplication I meant NSApplication.yieldActivationToApplication. Instead of NSRunningApplication.activate I meant NSRunningApplication.activateFromApplication. These corrections aside, I'm still looking for an answer to my original main question.

Please disregard. The installation scripts were deactivating an existing kernel extension before activating, hence the extra prompt.

It's pretty egregious that Apple would have a basic Javascript syntax error on their documentation page like that. The correct syntax is: title = choices['myapp'].title; Another quick note: if you print one of the values in choices, e.g. system.log(choices['myapp']); it will print (null) to the installer log, giving you the false impression that every one of these keys has a null value. This is not the case, and you can still access the values' properties, such as title, visible, selected, etc.

I have answered my own question: I am building codeless kexts wrong! There should not be any executable file, and the Xcode project should contain no source files at all, even empty ones. Once I built it correctly then there was no reboot requirement in Big Sur.

Sorry if I'm coming in here brimming with negativity, but it's never fun to wake up in the morning and see issues like this. The notarization requirement is bad enough as is, given that, in my opinion, it adds essentially no additional security to the platform, especially since there's already been at least one case of malware fooling Apple's notary into notarizing it. (Why not just check a quarantined executable for malware client side, rather than use a notary?!) But the fact that the notary service can't maintain consistent uptime just makes it painful. I can't send a build to a client now. Strangely Apple's system status page - https://developer.apple.com/system-status/ still lists "Developer ID Notary Service" as green.

I just exchanged emails with Apple developer technical support and was told that all Accessibility functions are only safe to call from an application's main thread.

I can offer a small tidbit of information, which is that I asked this exact question to an Apple engineer as part of a tech support incident, and while he wasn't willing to provide any information on timetables of feature deprecation (which is expected with Apple), he did say that codeless kexts are not mentioned in "Deprecated Kernel Extensions and System Extension Alternatives" at https://developer.apple.com/support/kernel-extensions/ So we can take that to mean that they will probably continue to be supported for at least a little while longer. Unless of course Apple has neglected to mention them in that document, which is totally possible.