In Google Colab:

pip install --upgrade git+https://github.com/kivy/python-for-android.git@develop

pip install --upgrade git+https://github.com/kivy/buildozer.git@master

In buildozer.spec:

p4a.branch = develop

android.ndk = 28b

Everything else remains the same as in your previous process.
No separate Cython installation is needed in this case.

Thanks to all developers involved in this issue as well!