External links hiding in data validation — find and remove them
The cells look clean of anything external — no formula references another file, and Break Links found nothing to break. But a dropdown list on this sheet is sourced from a range in a different workbook, and that's a data validation setting, not a cell formula.
What's different about this kind of link
A dropdown built with Data Validation doesn't put a formula in the cell — the cell just holds whatever value you picked. The list of allowed choices is a separate setting attached to that cell, and its Source can be a literal list, a local range, or a reference to a range in another workbook entirely. That external source is exactly as “live” as a cell formula link, but it's stored somewhere a formula audit never looks.
How to tell if this is what's happening
Click a cell that has a dropdown arrow, open Data → Data Validation, and check the Source field on the Settings tab. If it reads something like =[Products.xlsx]Sheet1!$A$1:$A$50 instead of a local range or a typed list, that validation rule is pulling from an external workbook, and Excel will keep flagging the file as having external links even though no cell formula does.
Fixing it without breaking the dropdown
Copy the source list's values into a local range in your workbook (a hidden helper sheet works well), then repoint the validation Source to that local range. Repeat for every validated cell — data validation isn't always applied to a single cell, so check whether it's been applied to an entire column. Upload your file below and the tool flags every validation rule with an external source, including ranges applied to whole columns you might not think to check by hand.