|I'm not sure why you posted basically the same question twice, so (as moderator) I have deleted your earlier post.|
That said, you can not use a formula to accomplish your goal. You need to use a macro and you need to save the file as an xlsm or xlsb filetype.
1 - Right click the sheet tab where you want to enter the 2 in A1 and choose View Code.
2 - Paste this code into the pane that opens.
2a - You must paste the code into the VBA Editor for each sheet in which you want this happen.
The code will monitor the entries made in the sheet(s) where the code is stored and when it sees a 2 in A1, it will Activate G6 on the 3rd sheet in the workbook.
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$A$1" And Target = 2 Then
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