Hi IM Tanuki,
As per your description, please don’t worry we can work together to narrow down and resolve the situation.
First, I can confirm I meet the same behavior as you described above.
For different workbook:
I understand when we make changes in different Excel workbooks and want to undo the changes only in the current workbook, use Undo will undo changes in other workbooks as well.
The UNDO operates only on the active worksheet. When works with multiple workbooks open, at the same time. If make some changes in one workbook, then start editing a different one. The undo stack seems to apply across workbooks, Excel maintains only one undo-stack for all open workbooks together.
As workaround starting another instance of Excel for each workbook. To open a new instance of Excel, enter Excel.exe /x in Search box next to the Start menu and press Enter.
For different worksheet in a one workbook:
First, I humbly request you please don’t mind and I apologize for it.
As your concern, “ Is there a way to isolate the undo stack on a per worksheet basis?” as I can confirm I also meet same behavior like yours and after my different test and search a lot unfortunately, I’m sorry to say that I cannot find a way to use Undo as per worksheet basis in Excel app.
Regarding to your concern, to improve the Excel view and this type of change has come up, you brought a brilliant point. We do understand your feeling that it would be very convenient if there an option in Microsoft Excel to Undo as per worksheet basis. As we listen to all feedback and consider them for additional feature/future versions of our products, and we requested you our feedback portal of Microsoft Excelto related development team so that they can get notice about it. Your feedback helps us know which features are most important to you.
I appreciate your understanding and stay safe!!
Best Regards
Waqas Muhammad