You're right, I haven't read them all, but didn't do it knowingly either. I did get an answer, however:

9_11_did_bush:
First I would make a helper column that with =IF(B2="", A2, B2) that transfers over whichever column is not empty. image

Then you can sort using the helper column and sku: image

source: 9_11_did_bush from reddit