The Computer Graphics Shaders class (link) taught by Prof. Mike Bailey of Oregon State University offers an advanced course on OpenGL and Shaders. This link connects with a further discussion of Shaders. I do not have a Github repository as yet that has a focus on OpenGL shaders on Android. Stay tuned.

The learnopengl.com web page discusses a broad spectrum of graphics topics. It is written in C++. I have ported the exercises to Kotlin and Android. Click here for a discussion and links to the Github repo that implement some of the exercises.

The book OpenGL ES 2 for Android: A Quick-Start Guide written by Kevin Brothaler is a great starting book for learning OpenGL. It is a bit dated now relative to other resources, but the examples still compile and run fine on Android devices. Click here for more background on the exercises.