Hello ZTS,
Microsoft has acknowledged this issue under incident OP1470668: “Users may be unable to copy, paste, drag, or duplicate cells and worksheets in Microsoft Excel.” The notice includes Excel 2021, so the reported impact covers both cell operations and worksheet copying.
According to the September 16 incident update, a code regression in a recent update caused the issue. Microsoft is testing fixes and evaluating an additional workaround. That update does not confirm a released fix or a resolution date.
As the forum’s AI recommended, you can try Home > Paste > Paste Special for cell data, using options such as Formulas or Values. This is documented in Microsoft’s paste issue article, but it does not replace copying an entire worksheet.
Since you have confirmed that reverting to build 16.0.14334.20848 restores functionality, please coordinate with your IT team if you need to remain on that build temporarily, considering the security updates it would exclude.
Your administrator can follow OP1470668 in the Microsoft 365 admin center under Health > Service health. The notice schedules the next update for September 17 at 19:00 UTC; this is a progress update, not a promised fix date.