Alternative - Connecting to Arbitrum with Chainlist (Connect at your own risk!)
Use Chainlist on your own risk! This is not the official tutorial but an alternative to consider by the open source community and promoted by Andre Cronje!
If you want to try a faster way for adding the Arbitrum One Mainnet information to your Metamask wallet you can use chainlist.org.
Chainlist is a list of EVM networks. Users can use the information to connect their wallets and Web3 middleware providers to the appropriate Chain ID and Network ID to connect to the correct chain. Andre Cronje's pinned Twitter message includes chainlist.org, and the source code can be found on the website of chainlist.org
By connecting your Metamask wallet to the chainlist.org, find ChainID 42161 (Arbitrum One) Currency AETH and add click on "Add to Metamask" to add the networks to your Metamask.