You can sign in to Monarch using your Google Account or Apple ID which has the advantage of not needing to remember a separate specific to your Monarch account.
None of your financial information is shared with Apple or Google if you use their sign in methods. It is just an easier way to sign in. We strongly recommend you use MFA or a 2nd factor authentication on your Google or Apple account so they are as secure as using Monarch directly with a password and MFA.
If you use first created your Monarch account using Google or Apple you will need to to hit the "Create password" button to disconnect from Google or Apple and sign in to Monarch directly: