Hello
I have the following Data Validation formula that creates a dependent list dropdown. It's complicated because it's designed to remove blank spaces.
=OFFSET(Backup!$AK$1,1,MATCH($C$9,Backup!$AK$1:$EC$1,0)-1,COUNTIF(OFFSET(Backup!$AK$1,1,MATCH($C$9,Backup!$AK$1:$EC$1,0)-1,100,1),"?*"),1)...