DevonTechnologies enforced using Light-Mode by setting a flag called “NSRequiresAquaSystemAppearance”. I don’t know why they do this.
You can change that.
open Terminal.app and enter:
defaults write com.devon-technologies.agent NSRequiresAquaSystemAppearance -bool NO
restart DevonAgent
for unding this enter:
defaults delete com.devon-technologies.agent NSRequiresAquaSystemAppearance
I am using Dark-Mode for DevonAgent w/o any problems.