Can't edit cells in Excel 2010 since Sept 2026 patch Tuesday

Before reversing any update, establish whether editing fails in every workbook or only particular files. Try a new blank workbook and note the exact message or behavior. For an affected file, check whether it is read-only, in Protected View or on a protected worksheet; do not bypass protection on an untrusted file. Then compare Excel started with excel /safe to isolate add-ins and startup customizations. Your Windows-update assumption also needs clarification: end of ordinary Windows 10 support does not mean every component stops receiving every kind of update, and eligible ESU devices can still receive security updates. Office and Windows updates are separate products. Excel 2010 itself reached end of support in October 2020, so a current supported fix cannot be assumed. Preserve the files, collect the Windows edition and update identifiers, and plan migration to supported Office rather than making security-update removal the default solution.