For each wallet, we will get the provider with useRpcProviders, to fetch the balance by calling the getBalance with the wallet address. 
import { useUserWallets } from '@dynamic-labs/sdk-react-core';
import { useRpcProviders } from '@dynamic-labs/sdk-react-core'
import { evmProvidersSelector } from '@dynamic-labs/ethereum-core'


const App = () => {
  const userWallets = useUserWallets();
  const { defaultProvider } = useRpcProviders(evmProvidersSelector)

  useEffect(() => {
    userWallets.forEach(async (wallet) => {
      if (!wallet) return;

      // Get the EVM Mainnet provider
     const provider = defaultProvider?.provider;

      if (!provider) return;

      // Fetch the wallet balance
      const balance = await provider.getBalance({ address: wallet.address });

      console.log('balance', balance.toString());
    });
  }, [userWallets, defaultProvider]);

  ...
}