I seem to have a bulb-like thing on the top part of my onion stems?
Certified GKH Gardening Expert
These are seed pods. Pinch them off. It will force the plant to focus more energy on the bulb and help it grow larger. You can also plant them if desired. Generally, the pods house the onion seeds and are normally dried to remove and grow these seeds. Here is more information: https://www.gardeningknowhow.com/edible/vegetables/onion/collecting-onion-seeds.htm