For me, 12.5.1 doesn't fix the slow debug speed. I redo my tests/measure again, but with ne Xcode 12.5.1 release. I didn't see any improvements at all: On the test machine macOS 11.2.1 with Xcode 12.5.1, Starting application in debug took 25s. macOS 11.4 with Xcode 12.5.1, it take between 85s to 135s (3.5 to 6 time slower)