Here is the item again:
Coated with dust, (A)
the blinds filtered shadowy light into Adrian's cluttered
apartment, (B)
where clothing and empty take-out boxes littered the
floor. (C)
As flies buzzed around rotting bananas on the kitchen counter.
You correctly realized that the period after floor was wrong. As flies buzzed around a rotting bunch of bananas ... is a subordinate clause. When you attach a subordinate clause to the end of a sentence, you generally need no punctuation.
To fix the problem, you chose to do this:
Coated with dust, the blinds filtered shadowy light into Adrian's cluttered
apartment, where clothing and empty take-out boxes littered the
floor as flies buzzed around rotting bananas
on the kitchen counter.
You have correctly employed Punctuation Rule 1:
Main clause + Ø + subordinate clause.
You deserve cheering fans!