The Microsoft Edge use device theme is using the light theme on Ubuntu

Version 124.0.2438.2 (Official build) dev (64-bit)

On sites where you can select use device theme (like youtube), Edge uses the light theme by default, although in Ubuntu I use the dark theme.
This is not a Chromium bug because they fixed it a long time ago:
https://issues.chromium.org/issues/40642550#comment176
I can confirm that Google Chrome detects the theme correctly in Ubuntu.