Try this Non-VBA solution:
Move the formula from G2 to another cell, say K2... then create a list using a formula and K2 result.
So, in L2 enter formula:
My Formula:
=TRIM(MID(SUBSTITUTE($K$1,",",REPT(" ",100)),1+(100*(ROWS($A$1:$A1)-1)),100))
and copy down as far as you need to make sure all possible entries A7:C7 are included.
Then go to Formulas tab, then select Define Name, enter name like: MyList and then in the Refers to box enter formula:
My Formula:
=Plan1!$L$1:INDEX(Plan1!$L:$L,COUNTIF(Plan1!$L:$L,"?*"))
Then use Data Validation with List choice in G2... and enter, in the source field:
My Formula:
=MyList
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