As the title said, I totally know how to build a DApp and connect to Metamask, and this day a new mission is to build an Ethereum wallet.

Suddenly switch to the other side, one thing that I am confused about is how Metamask and Trust wallet connect with the DApp? Is there a standard?

Maybe it can be sperate into 2 answers, one is the Mobile App solution and the second is Browser Extension (BEX)