If you are on MD2021, Try this. Get the latest preview build 3066. Download and install my extension net-account-balances. In the Config screen, select all accounts (not categories). Does that value (on the Home Screen widget) match the crazy total you are seeing? Report back with your findings.
If it does match, you can try selecting combinations of accounts to find the crazy balance.
Your example does not look like the default reminders display on the summary. I don't find the total on the bottom as you show. Can you describe the source of your example? Seems like the issue is with amounts set up in your reminders.
I don't have the tech skills to find and install preview builds, and fear really messing up the file by poking around in it. I have tracked data back to 2003, and find large balances in old 'inactive' accounts.
I decided to start a new MD file, dated May 1, using the most recent bank account statements, and archived this $trillion database, in the event I want to search account activity prior to May 1, 2021.
I will chalk this up to failure to properly account for investments and the transactions therein. Thanks to all for your input!