What can be happening to my flowers. I plant these same flowers every year in these pots. I am watering these for 5 minutes every morning which is what I do every year. I don't think it's too much because the water runs out of the bottom of the pot so I don't think they are waterlogged. There's an ivy in the pot as well.

What's happening? Is this a fungus or a bug???

looks like fungus. Happened to me this year. I put a thick layer of mulch in the landscaping and planted flowers right after (party coming up the next weekend). Rain that week and soon after the plants started dying and mushrooms popped up. I assume the mulch had fungus and the rain kicked it off. Some lived some died. Should have waited a few weeks for the mulch to settle in, but did not have the luxury with the party.

Reduce watering and see if they live, otherwise wait a few weeks and replant.

Or pill bugs and / snails, they'll devour plants like that. Check them with a flashlight around midnight. My poor marigolds :-(. Pick up some Sluggo Plus as a tasty treat for them.

https://plantdiseasehandbook.tamu.edu/landscaping/flowers/zinnia/

If they were my flowers, then they would say root rot, since I tend to overwater.
I do better with MiraclGro fresh potting mix, the old goes into hedge beds, around trees.
Rainwater best, R.O. might be OK
SOAK twice/week and never if pencil comes out wet if pushed in deep.

Black thumb here, quoting from Garden Success KAMU-FM pro advice