On 8, Microsoft rolled out KB5002914 for Excel, but it apparently has a bug that makes it impossible to copy and paste.
A September security update silently killed copy and paste, autofill and formula dragging in Excel.
Microsoft has fixed a known issue that causes copy-and-paste failures for Excel users after installing the September 2026 security updates.
Microsoft's September security update stops Excel from pasting. The command fails without a beep and without an error message ...