Kernel Extensions are gone -- regular users would never care about this sort of thing but you can't use products like Little Snitch properly on Big Sur and onwards. Kexts were also used for making Hackintoshes -- again not something normal Apple users would care for. mac OS is simply becoming less versatile and more locked down.
Well, Hackintosh users at least definitely don't care whether Apple is signing third party kexts, because they were never signing Hackintosh kexts anyway. The ability to load kexts in general is still used extensively by Apple and isn't going away any time soon. (Hackintosh's days are numbered anyway due to Apple Silicon.)
