You can stake $MATIC on Celsius Wallet (mobile 14% APY). Also, PoolTogether is giving away $MATIC rewards for joining their pool: https://medium.com/pooltogether/pooltogether-aave-polygon-e867879c3e9b.

Celsius – 14% APY:

 

Pool Together USDT / Polygon $MATIC Rewards: https://app.pooltogether.com/?filter=polygon&tab=pools.