Files specified in MANIFEST.in ignored when creating a python package

Maybe I'm already too tired (it's already late) but I'm not able to find out why files specified in MANIFEST.in are being ignored, even though include_package_data = True is set.

Here's my training setup:

.
├── config
│  └── conf.yaml
├── MANIFEST.in
├── pyproject.toml
├── setup.cfg
├── setup.py
└── superapp
   ├── __init__.py
   └── main.py

setup.cfg:

[metadata]
name = superapp
version = 0.1.3
description = My superdupermega app
classifiers = 
    Programming Language :: Python :: 3


[options]
zip_safe = False
include_package_data=True
packages = find:
install_requires = 
    loguru
    pyyaml

[options.entry_points]
console_scripts = 
    gaga = superapp.main:main

MANIFEST.in

graft config

pyproject.toml

[build-system]
requires = ['setuptools>=58.3.0']
build-backend = "setuptools.build_meta"

Yep, I know that this might be a classic, but I'm really out of ideas. I know that there's still the option to use package_data as well, but shouldn't include_package_data do the trick? Neither python setup.py sdist nor python setup.py bdist_wheel included config.