I can understand the desire to not worry about the system dark mode and just do things with the normal colors and styles. Keep in mind though that your user is the one who decided that they wanted to use dark mode, and forcibly ignoring that could be perceived as saying that you don’t care about your users.
OSX dark mode is better supported in wxPython 4.1. There will be an official release soon, but in the meantime you can get snapshot builds from https://wxpython.org/Phoenix/snapshot-builds/. You can either download an appropriate wheel file from there, or you can have pip download and install it with a command like this (for Windows or macOS):
pip install -U --pre -f https://wxpython.org/Phoenix/snapshot-builds/ wxPython
Remember that this is not a released version, but lots of people are using it already.