Prickly lettuce. It's an annual.

Pull and discard/compost before the seeds blow everywhere or you'll have a bazillion more next year.

Awesome! Am I correct that I should only be concerned with those with seed pods and about to flower like my second picture?

In a month, we'll get our first frost. I hope, they'll get killed.

Just mow them off when you mow the lawn. That will keep them from going to seed and their numbers will soon diminish if you prevent seed production.