Excel repair strips all formulas from large .xlsm after March 2026 security update (KB5002849)

Libre-Office can be useful for opening a damaged workbook without immediately accepting Excel's repair prompt, but I would not use it to repair or re-save a model that depends heavily on LET, LAMBDA, XLOOKUP, and VBA. Its formula compatibility is different, so a file that opens there can still change meaning when it returns to Excel.

For this case, Excel remains the correct target environment and the safer comparison is between an untouched original, a known-good OneDrive version, and a copy opened offline with AutoSave disabled. Preserve the original .xlsm as read-only, download earlier versions rather than restoring over them, and collect the repair log for Microsoft support. A generic spreadsheet recovery product may promise to recover formulas, but it is unlikely to understand the model's modern functions better than Excel itself.