People have a lot of misconceptions about eating sprouted onions, but the reality is that eating sprouted onions won’t hurt you unless you have a sensitive palate.
However, the flavor will be a bit different, becoming much more bitter and significantly less sweet since the onion uses the sugar stored in its cells to create the sprout.
Sprouted onions have the sharpness and bitterness of red onions due to the loss of sweetness and work better than fresher onions in vinegar-forward dishes like pickled onions.
You can also mellow the flavor of a sprouted onion by rinsing or soaking it in water or removing the sprout itself to negate some of the bitter flavor.