Excel keeps inserting an old formula I don't want. How do I stop this?

I have a strange problem. Whenever I start typing a formula in a new cell, Excel automatically suggests and inserts an old formula that I used months ago in a completely different workbook. It happens after I type the equals sign and the first letter. For example, I want to use SUM, but Excel fills in a long SUMPRODUCT formula from an old project. I have tried clearing the recent formulas list and turning off Formula AutoComplete in Options, but the behavior still happens.

Does Excel store formula history somewhere outside the current workbook? Could this be a cache issue or something related to my account syncing across workbooks? I am using Microsoft 365 on Windows 11. This does not happen on other computers, only my main machine. Any help would be great.