wiring - is this feeding other circuits or all switches?
The cable with the white wire in the black wire bundle goes to a switch and the single black wire is the switched hot.

The others feed through to something else.

The National Electrical Code requires junction boxes to remain accessible. So you can't cover it up.

However, they do make a Code-compliant splice device for NM cable that could be covered up. It is designed for only one cable though. So, you would have to remove enough of the existing wiring so you only have to splice one cable.

Or, you can rewire the circuit to move the J-box elsewhere.

Good luck!