This page explains how to fetch accounts from a Web3 provider.

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Getting Ethereum accounts with EIP-1102

Use EIP-1102 to obtain authorization and get Ethereum accounts. Invoking EIP-1102 shows a QR code dialog if the user’s mobile wallet is not already connected to your app. The following code runs in response to a user-initiated action such as clicking a button to ensure the pop up is not blocked by the browser. 
// Use eth_requestAccounts
ethereum.request({ method: "eth_requestAccounts" }).then((response) => {
  const accounts: string[] = response as string[];
  console.log(`User's address is ${accounts[0]}`);

  // Optionally, have the default account set for web3.js
  web3.eth.defaultAccount = accounts[0];
});

// ethereum.enable() is now deprecated in 4.0.0
ethereum.enable().then((accounts: string[]) => {
  console.log(`User's address is ${accounts[0]}`);
  web3.eth.defaultAccount = accounts[0];
});
Once the user obtains authorization, the Web3 object (web3) and the Web3 Provider (ethereum) are ready to be used.
If you were using ethereum.on("accountsChanged"), remove it and obtain addresses with EIP-1102 callbacks instead. It was removed to improve compatibility with the latest web3.js.
Next steps: