Apps like Universal Copy (https://play.google.com/store/apps/details?id=com.camel.corp.universalcopy&hl=en) can copy "not selectable text" from Android apps. How can one prevent this?
The app uses OS accessibility features to grab content from text fields. Can we add anything to manifest so this app can't copy texts?
I'm not at all an androit expert but the answer is probably no, you can't prevent text from being copied, and it's good if it is so. Anyway, it's a very very bad idea.
Remember when there was scripts that tried to prevent images from being copied by intercepting the right mouse button click. In fact it didn't prevent anything, since power users had other tricks to save the images by another way. It was just frustrating for lambda users.
Preventing whatever displayed text from being copied is the same sort of "protection". It's just annoying, without really preventing from anything.
You'd better to always keep in mind that, everything you send to the network and displayed can be stored, copied, modified and be further sent to anyone. It's true for music, it's true for photos, it's true for videos, and it's also true for simple text. The only good way to prevent a certain part of unwanted copies is with watermarking techniques.
Whether you like it or not, it's so. IF your work is really worth it, it will eventually end up available for free somewhere.
Give me a real true good reason to prevent your text from being copied, and I will immediately delete this answer.