All the dead and diseased leaves from last year are "clogging up the works". Its too big to rake out by hand, so either hire someone to power rake it, or get a thatching blade for your mower. ......Bag all the clippings, and fertilize.

Makes sense but I don’t have any leaves in the front (no big trees).

would you still recommend a power rake or aeration?

I've had just as bad in the past. it'll likely all come back just fine. that seems doable to just rake by hand? i wouldn't even rake it up but just to let it get some air under there.

It resembles snow mold to me, google snow mold

Yep , its probably got some snow mold, but the conditions for this disease are going away, and the new grass blades need some more air and light circulation to fill in the damaged areas. Both de thatching and aeration would be ideal. lawn care companies are busy this time of year doing this very thing.

To prevent snow mold next year, apply fungicide in the fall, along with a 'winterizer' type fertilizer. Also lower the mowing height to correspond with the lower sun angle and cooler temperatures .

I remember this lawn. You did a nice job with it. My understanding is that new lawns are more susceptible to snow mold. The only snow mold that is dangerous to the lawn, I believe, is pink snow mold. The rest you can forget about. I'd love to see someone aerate and dethatch (usually useless unless you actually have too much thatch) only half their yard and take weekly pictures of what differences there are. It would be very informative to the aerate/don't aerate opinions.