Onions are classed as long day, short day and intermediate. If you are upper Midwest you want long day onions or intermediate.
I’ve had the best luck with starting from seeds indoors, or planting the dormant plants (not bulbs) sold in bundles at the local farm store. But, only tried bulbs once, so not a lot of experience with those.
A friend of mine lamented that her onions would always rot. However, she also shared that to get green onions, she thought you just clipped off the tops of your growing onions. Nope, you grow onions for that particular purpose. Don’t clip the tops off of the onions bc water gets inside the layers that way and will rot your onions.
I plant a bit close, then pull green or baby onions as they grow to give more room to the ones I leave in the ground.