Setting up a network via Chainlist.org

Go to chainlist.org, select the network, in this example we'll choose "Polygon Mainnet", and click "Connect Wallet".

In the pop-up window of the MetaMask wallet, confirm the connection of the wallet by clicking "Next", then "Connect".

Then click “Add To MetaMask”.

Then confirm the addition of the network by clicking "Approve", then "Switch network".

Done!