Django / makemigrations ModuleNotFoundError: No module named 'idmp_core.apps.IdmpCoreConfigdjango';

You just forgot to put a comma in there

Here you go

INSTALLED_APPS = [
    'idmp_core.apps.IdmpCoreConfig',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]