This video is straight to the point tutorial on installing a subwoofer on your 11th gen civic. I will link some of the items I used in the description or better alternatives!

Amp Install wiring kit : https://a.co/d/f58oSxl

Skar SKv2-1500.1D Amp : https://a.co/d/cl1YIP9

They have changed the Line output convertor to a different brand still should plug in and work no problem.
11th Gen Civic 7” harness : https://www.ebay.com/itm/143447122926...