Thanks for providing the screenshots. Doesn’t that change all assets that are imported in my project? I want to be able to switch quickly between building for windows and building for android.
In the image on the right (the Importer settings in the Inspector after selecting all/however many textures), you should be able to pick Android tab, then set the Max Size - this will only apply to Android
I’ve used 2018.4 in the past and did have the option, plus in versions before and after that. I use the tabs more for setting the texture quality, since Unity removed some commonly used options from Default for reasons that were supposed to reduce user error, but increased them massively for me, and others I have spoken to.
Just to be clear, in polemical’s second image, you will see a tab saying “Default”. Next to it are tabs for the other platforms. Unfortunately Unity uses icons, not names for those, so it is not as clear as it should be. Go to the Android tab and you should find an option for max texture size.