On 8, Microsoft rolled out KB5002914 for Excel, but it apparently has a bug that makes it impossible to copy and paste.
Microsoft has confirmed a copy-and-paste issue affecting Excel 2024, 2021, 2019, and 2016 after the KB5002914 security update ...
Microsoft has fixed a known issue that causes copy-and-paste failures for Excel users after installing the September 2026 security updates.
Microsoft has confirmed that copy and paste may silently fail for some Excel users after installing the 2026 KB5002914 ...
A September security update silently killed copy and paste, autofill and formula dragging in Excel.