Could we have a closeup, preferably in the evening in shadow or in overcast, of those brown patches? I suspect fungal disease.

I'm thinking the beginnings of brown patch, a fungal disease. I'd also suggest getting confirmation of that.

But a good shot of DiseaseEx from the Big Box Store local to you (or any other good wide-spectrum antifungal) would both take care of it and protect the grass against future fungal diseases for a couple of weeks.

What is your watering schedule? How often and for how long do you water?

Haven’t needed to water a lot since we’ve had so much rain but if we don’t have rain for around 2-3 days I turn on the irrigation system for 15-20 minutes in the evening. am I watering too much?

Yes. :-) Try to back off to 4 days right now, then work it back slowly to 5 as the grass adjusts in a few weeks. Then 6 if you can and, eventually, 7 as the season rolls onward.

Weekly deep watering is the ultimate goal. It'll lead to less disease and a much healthier lawn that can access more water and deeper resources using deeper, denser roots.

And 15 to 20 minutes isn't right either. Let the grass dry out a few days and then place some cat food or tuna cans around the yard. Turn on the sprinkler and time how long it takes to fill the cans. The time will surprise you. My oscillator sprinkler takes 8 hours to fill the cans. But once the grass gets 1 inch of rain, it should not need to be watered again for a week or more as the deeper roots pull moisture from much deeper in the soil. If you've been watering daily, you'll have to wean the grass off of that frequency. Your grass has short little roots because it doesn't need to go deeper. So for you, you can deep water and watch it to see when it starts to wilt. Then deep water again. Soon enough you'll be on a weekly schedule that makes the grass a lot greener with much less chance of disease.