Is it possible to apply and show dark mode to apps even if the OS is selected as light mode.
This is not possible currently without building your entire UI using Canvas or possibly with Declares.
@Sam_Rowlands might have something in OAK or know the declares.
For the macOS I do indeed, but only the macOS.
Take a look at the demo application for the App Kit 2021 - Building Better Mac Applications it allows you to change the “Theme” on the fly or force a Mac application to use one of the 4 available themes (don’t get too excited, two are just variants).
Thanks @Anthony_G_Cyphers for prompting me.