bitcoin feeless transactions – Bitcoin Stack Exchange

The mobile application cashapp specifically says I can send bitcoin to any address anywhere in the world for free.

Coinbase also says they can do off the network transactions instantly and for free as long as both parties have a coinbase address…how does this work ? Does a miner check these transactions ?

Where does the concept of average transaction fee come into place ?
https://ycharts.com/indicators/bitcoin_average_transaction_fee