"The second, runs from the attic."

What is this wire connected to in the attic? You wrote that the black wire from the circuit breaker is connected to laundry room switches in addition to this one. Is there an outlet or switch in the attic that also receives its power from this circuit? If so, then follow the Single-Pole instructions:

• Connect black wire from circuit breaker AND black wire to attic to the black wire on the dimmer.
• Connect the black wire from the lights to the red wire on the dimmer.
• Connect the ground wire to the yellow+green wire on the dimmer.
• Cap the red+white dimmer wire.

I followed the instructions and the attic light and outlet are back. Thank you. Now the problem is that the kitchen light (connected to the red) is not working. I tested the red wire with a non-contact voltage detector, but it's getting none.

Bypass the dimmer by connecting all three black wires together. Does the kitchen light turn on?

Yes, the kitchen light works, but the switch doesn't. Does that mean it's dead?

I can't read the photo of the instructions, but what do they say about the two red wires on the dimmer (I assume that's what I'm seeing in the bottom photo)?

In a Single-Pole scenario it says, "connect the red dimmer wire to the load wire removed from the switch". In case of 3-way, "connect the red dimmer wire, red and white dimmer wire to the remaining 3-way switch's two wires removed from the switch.

One of your black wires feeds the kitchen light and another black wire feeds the attic. The third black wire is the power from the breaker panel. To find out which is which, if you are comfortable doing so, you can remove the dimmer and separate the three blacks and make sure they don't touch each other nor anything else. Make sure no kids or pets are around, and turn the circuit breaker back on. Check CAREFULLY which one of the three blacks is hot. CAREFULLY mark this wire, and shut the power off. Connect one of the two remaining blacks with the one you just marked, and turn power back on. Note what is now on: kitchen light or attic. Turn power off. Identify this wire accordingly. The remaining black wire feeds whichever did not get power in the previous step.

The wire that you have identified as feeding the attic should be twisted together with the black wire you have identified as the power from the circuit breaker and the black wire from the dimmer switch. The red from the dimmer switch should be twisted together with the remaining black wire. Keep the red with a white stripe capped and the green/yellow connected with the bare ground wire.

"Yes, the kitchen light works, but the switch doesn't. Does that mean it's dead?"

Maybe. What is the brand and model of the dimmer, and what kind of bulb does the kitchen light have (LED, fluorescent, incandescent)? They may be incompatible.

MEW-DM660 dimmer switch + Recessed LED lights. They used to work just fine until I noticed the issue in the attic. I'm thinking I might have blown it out because while trying to wire it earlier, before posting here, the circuit breaker tripped immediately after turning it on.

Yeah, the Maxxima MEW-DM660 looks like it should work if your LED light is more than 4.5 watts as noted in the instructions AND IS DIMMABLE. I use Lutron LED+ dimmers; you might try the Lutron CTCL-153PDH-WH Skylark Contour LED+ Dimmer Switch -- if you need a replacement.