What is the difference between Mainnet (GQL) and Mainnet (ADL) and how to change the transport?

By clicking on the transport name at the top of your screen, you can change between various networks.

GQL is main.ton.dev

ADNL is a backup transport in case of problems with GQL

In general, the difference is that GQL works faster, ADNL is a simple RPC server for a C ++ node, it works slower, but it can work with any node, in the near future we will publish it in open source and it will be possible to connect a wallet to your nodes. In general you can choose GQL, in case of problems the wallet should switch to ADNL itself.