Not sure what exactly you mean. There shouldn't be a need to close it off if it's underneath drywall. Just insulate all around and below it. If you really want to, you can use a can of spray foam, although I wouldn't because it's not necessary.

Spray foam in a can.

You should make an effort to better secure the wiring first. Wires should not be close to the face of the wall: too easy to put a nail in one. Our code officer would make us use fire-rated caulk and fit some boards around it, but the fire-rated "Great Stuff" foam would work. It is good to create a barrier to smoke and fire traveling from floor to floor.

Strap the wires down, as suggested. Then use fire-rated spray foam to close off the hole (its the red/orange Great Stuff foam in cans at the store). Code now requires you to close off the holes so they don't create a chimney for fire to spread from one floor to the other. In reality, you probably have other holes that have not been closed off, but its better to be safe.

When you spray the foam, use nitrile gloves and spray it in very gradually. It expands quickly and can drip or run into places where you don't want it. It is a real PIA to get off your hands or any other surfaces. Don't spray too much until you have given it time to expand and really see how much is filled. If you use rags to wipe off excess foam or protect a surface, plan to throw them away afterwards.

Bruce

Seabornman answer is good. Best to use fire-rated insulation and fire-rated spray foam if you decide to do that. This stuff is great: https://www.homedepot.com/p/Owens-Corning-R-15-Thermafiber-UltraBatt-Mineral-Wool-Insulation-Batt-15-in-x-47-in-UB-40-P3D-15-47-121/304633821

It has to be fire-rated material, so you can use Mineral wool insulation or Fire-rated foam as others suggested you can find it at local Box Stores.

I notice that insulation is unfaced. I planned on putting faced insulation between joists. I am not sure that I want to get a whole package of unfaced insulation just for that one little hole

The mineral wool insulation in the link above would go in the wall too. Also great for rim joists throughout the rest of the basement since it's water/mold resistant.

if I go with a mineral wool, do I need a vapor barrier?

I personally wouldn't. I don't know the latest best practices on vapor barriers, but because they restrict airflow and trap moisture, they can lead to mold growth and rotting behind them if water gets in, which it eventually will. I know my city took them out of the codes because of serious mold issues resulting in many lawsuits, especially in basements.