Does the Catalina XNU kernel still recognize 32-bit binaries? Does 10.15's dyld?
Does 10.15's XNU still recognize 32-bit binaries?


They are still recognized as executables, but attempting to execute one results in a "bad CPU type in executable" error, just as if you were trying to run an PowerPC or ARM binary (and different from an incomprehensible file, which will result in an "exec format error" error).


  Does 10.15's dyld still recognize them?


Recognize them as what? It'll recognize that an .dylib with a 32-bit slice is a library, if that's what you mean, but it'll refuse to load it into a 64-bit process.