I recently installed a dashcam in my 2014 Honda Odyssey Touring Elite. I wanted to hardwire the installation, so I spent some time testing with a multimeter to find an unused fuse space that was switched with the ignition. After much trial and error, I found that slot 22 in the passenger side fuse box (I think the Odyssey has at least 3 fuse boxes) was the best. It’s only powered when the ignition is set to “run” mode, not accessory mode. I found a ground screw nearby.
I used the Rexing Mini-USB Hardwire Kit https://www.amazon.com/gp/product/B01LXC2329/
Here are photos of my installation: