You literally said “what about” in your comment.
Do you legitimately think that any use of the words "what about" makes something whataboutism?
You specifically argued that the problem lay elsewhere
Again, you seem to have missed the point of the comment. I did not deny that Steam needs improvement. Things can be symptoms of larger problems, and calling that out is not whataboutism (to the contrary, the purpose of whataboutism is to suggest that there is no problem with item X -- not that item X is a symptom of item Y).
Edit: clarity