I would approach as follows:
1) Create named ranges in column AD, named with the brand such that named range "AP" is range AD2:AD6 , named range "AQ" is range AD7:AD9 etc
2) In cell B4 use data validation as List type, with the formula First time you type it in you may get an "Evaluates to an error" message, just ignore that.
You can lay out your named ranges however you like, I normally use one column per category.
The Indirect() function simply takes a string and tries to evaluate it to a range.
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