platformio.ini env_default=xxxxx has to match one of the labels in the...

platformio.ini env_default=xxxxx has to match one of the labels in the env:xxxxx, otherwise nothing happens when you `pio run`

platformio.ini

@@ -16,7 +16,7 @@ src_dir = Marlin
 envs_dir = .pioenvs
 lib_dir = .piolib
 libdeps_dir = .piolibdeps
-env_default = mega2560
+env_default = megaatmega2560
 
 [common]
 lib_deps = U8glib@1.19.1