site-packages/urllib3/__init__.py:34: NotOpenSSLWarning: urllib3 v2 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled with 'LibreSSL 2.8.3'. See: https://github.com/urllib3/urllib3/issues/3020

Turns out that urllib3 version 2 wants OpenSSL to work properly. The earlier versions of urllib3 version 2 even stopped entirely, the later ones throw this warning. But my current ssl module appears to be LibreSSL. The idea is to install an urllib3 that is compatible with LibreSSL.

Solution

pip install urllib3==1.26.20

An older version of urllib3 series 1 works, I picked the latest. Now my app runs without the warning.