(adsbygoogle = window.adsbygoogle || []).push({}); Hi, is there a way to use custom themes, or themes from .apks or the play store without a launcher?

There's just this **** kind of store with themes and almost none is free.

Android 7 has also almost no way to customize the background. Just pics or this pre-made themes.

I'm not sure on this one, but take a look at things like KWLP, KWGT, Launchers(Nova).... If you are looking for system level changes to themes (i think you are because of what you said try using google and the theme name to access maybe an external place where the .apk is shared)
As i am also A samsung user I will look into system level themes for you boss.

I dont really like launchers...

Which format have the S7 themes

idk bro.