Excel 2010 sometimes unloads non-default add-ins. Fix: In Add-ins dialog, check the box for XLOOKUP, then click OK . Then immediately save a blank workbook as your default template.
Q: Is the XLOOKUP add-in compatible with Excel 2010 64-bit? A: Yes, the XLOOKUP add-in is compatible with both 32-bit and 64-bit versions of Excel 2010. xlookup add in download for excel 2010 free download
Be very careful downloading "free add-ins" from random Google search results. Many are bundled with malware or adware. If you choose this route, ensure the source is a verified GitHub repository or a reputable Excel MVP blog (like the sites run by Excel experts such as Chandoo or My Online Training Hub). Excel 2010 sometimes unloads non-default add-ins