Only for the brief period of time they happen to be in line with it. For orbiting planets, we can see these occlusions happening multiple times and thus filter

Only for the brief period of time they happen to be in line with it. For orbiting planets, we can see these occlusions happening multiple times and thus filter them out from the noise, but there are countless reasons the light from a star could briefly dim once. We can find bodies within the solar system as they'll occlude multiple stars in a row as they move along, but for rogue planets to move far enough across the sky to occlude another star would take millennia.