Here is the original item:
Coated with dust,
(A) the blinds
filtered the sunlight entering 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 wanted to do this:
Coated with dust, the blinds filtered the
sunlight entering Adrian's cluttered apartment.
Where clothing and empty take-out boxes littered the floor. As flies
buzzed around rotting bananas on the kitchen counter.
Adding a period after apartment makes a fragment. Where clothing and empty take-out boxes littered the floor is a subordinate clause, which cannot stand alone as a sentence.
You might want to review the rules.