1. Download shadermod library from mcpelauncher-shadersmod releases.
2. Make sure to match arch for apk that you use in the launcher. For example, x86_64.
3. Extract the zip.
4. Open up your mcpelauncher folder. In Linux it would be /home/username/.local/share/mcpelauncher (Alternatively, you can open data folder from the launcher)
5. Make a new folder named mods and move the newly extracted .so file there.
6. In /home/username/.local/share/mcpelauncher make another folder named shaders and put all the shader material.bin files there. (You can get those from shader.mcpack /renderer/materials)
7. Now opening Minecraft from the launcher should load shaders succesfully. (Make sure you're using 1.20.80+ supported shader if you're playing newer versions than that)
TIP: Replace Linux paths as Mac if you're on Mac.
How to disable the mod?
1. Add .bak extension to the .so file that you downloaded.
or
2. Rename the shaders folder to something else. (It doesn't disable the mod but stops the mod from loading shaders)