I was told folding over the seed stalk to frustrate seed formation directs more of the plant's energy to bulb formation. Is there any truth to this? Sometimes, the stalk breaks entirely, probably not a good thing. What about snipping off the flower head at its apex?
Onions, Folding or Cutting Seed Head
If your onions are starting to flower, then they are past their prime. Once the onions start flowering, most of the sugars rush up to the flower making the onion kinda tarty not so much sweet. good luck! They make pretty blooms
These articles should help: https://www.gardeningknowhow.com/edible/vegetables/onion/onion-info-tips-for-growing-big-onions.htm