Install Android Studio on your PC and create a new empty app. Plug in your mobile and deploy that app. Now select that app as the second one for the lower half. It should be all black, if its all white, change the background color.
Or look if there is an all black app in the store, probably a screen tester app.
Samsung has this feature build in and its called ‘Extra dim’ or similar. Its a quick setting one can get when customizing the tiles.
I used to use third party apps too, but it was annoying that you couldnt grant permissions or install new apps without deactivating the dimming app since it was a security risk to have an app which draws over other apps.
Never heard of geopdf but i found this:
https://help.locusgis.com/support/solutions/articles/47001094929-how-to-import-geotiff-or-geopdf
So you can convert your files with qgis (free) on a computer and than have a broader selection of apps like locusgis. You could also try locus (non gis) or osmand which is foss.
I like what other people describe as ‘bloat’ on a Samsung. But I am a powetuser who actually uses a lof these functions. Sure i dont need two calenders. But i can just not activate the samsung one and hide it in the launcher. Also i would say that samsung has a better ecosystem. I am also using a samsung tablet which is superb and some samsung smart tags. If you get a pixel you dont really have an option to use any working smart tag.
I know of two ways:
Use a virtualization app like Parallel Space (Play Store). The way I understand it is that it creates some kind of virtualization where you can clone your installed apps into. They than work independent from each other.
Alter the package name. Apps are distinguished by package name. When you alter it for an apk you can install it without overwriting the app with the original apk. Revanced Managar (found on github) should be able to do this. I wasnt successful with it though the last time i tried. But I bet that there are working solutions out there.
Whats a github client?