Parts of your description are confusing. You talk about a textbook but then talk about clicking OK. Where is the OK that they are going to press?
this textbox should appear in all 30 sheets, whilst this textbox is on we should be able to work on other sheets as well.
If the user attempts to save, this textbox is generated in all 30 sheets? I think your best bet there is to create these textboxes in each sheet but make them invisible. Then the code can just make them visible. I recommend using a Textbox control instead of a textbox shape so it can be more reliably addressed in code.
Here is the basic idea but I suggest you see if you can adapt this. Instead of generating textboxes in all the sheets this code just shows a message box.
Put the following code into the ThisWorkbook module:
And in each existing button handler:
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