from time to time, I got out in the sun and need a light theme for that.
So I mostly switch to Breeze and hope, that everything comes along with it.
I found some tips here: Dark mode switching - ArchWiki
For example switching to another Firefox theme to make it go along with the system theme changes.
What I could not figure out though was how to change the theme of Konsole/Yakuake.
Though the borders of the windows changed, the content did not.
I am probably on the wrong track asking for advice on how to change the theme for Konsole/Yakuake, as it is probably a profile inside Konsole and or the fish shell itself, that needs changing.
I hope you are getting what I want to do. Else, please ask so I can try to clarify.