This question is an exact duplicate of:
While we're waiting for the Android app to be repaired ...
The browser UI lets us set both most and least favorite tags, and set a filter to hide questions carrying the latter. In some stacks I found that quite useful as a way of focusing on the questions I could actually contribute to or learn from.
As far as I can tell, the app doesn't have that filtering capability, despite needing it more due to smaller screens.
I presume it's on the list for eventual implementation. But sooner would be nice.