|I think we need more information related to what you mean by "change flowchart".|
If you are talking about changing the text in a text box on one sheet and having it change the text in a text box on another sheet, then that is possible. Cumbersome, but possible. You can set up a text box so that it refers to the contents of a cell. When you change the contents of the cell, any text boxes that refer to that cell will reflect that change. It's cumbersome in that you are not actually typing in the text boxes so you have to remember which cell(s) the text box(es) refer to. I'm sure that there are creative ways to accomplish this so that it is relatively "easy" to do.
For example, this is one of many sites that explain how to set up a flowchart and refer to cells for the text box contents.
However, if you talking about changes such as dragging text boxes and connectors around in Sheet1 and expecting Sheet3 to mimic those moves, I can't imagine that Excel is capable of doing anything close to that.
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