> This is quite curious. Apple inconvenienced so many users by "removing" 32-bit support on Catalina, and then they added support for local descriptor tables? I'm not aware of any use of LDTs on modern systems (except perhaps Chrome for additional sandboxing).
For the specific purpose of enabling CrossOver's 32-on-64 support and things like it.
It's not too hard for the kernel to support user code merely entering the processor's 32-bit mode. CrossOver's processes don't even use 32-bit system calls or 32-bit Mach-O binaries, so support for those could hypothetically be removed, except that most of it is needed for watchOS anyway. But the most significant cost of i386 support was in userland, not the kernel: building separate x86_64 and i386 copies of every system library, and supporting the legacy i386 ABI, including an older version of the Objective-C runtime ABI. That's all gone now.
The Classic Environment (OS 9 -> OS X) was dropped after 6 years.
Rosetta (PPC -> i386) was dropped after 5 years.
i386 -> x86_64 is now being dropped after 12 years.