What's the best way to cover up a metal electrical panel box?

Paint it the same color as the wall. Then hang art over it so that it is easily removable when you need to access the panel. May not be pretty but necessary!

https://www.pinterest.com/pin/135459901262252043/

You can paint it with chalk paint and put trim molding around the outside to make it look like it is a picture frame. Then you can use the chalk board to write notes on, let kids draw on, or draw a pretty picture.

I agree with Naomie..hide the panel but have quick access to it.

I also got a framed poster with open back, frame is about 1/2" larger than electrical box, fits perfect and looks great

Have you considered putting a kitchen cabinet over it?

I saw a while back where someone had taken a old drawer, painted it to match the walls, placed a poster/picture bottom, made a frame around the picture and hung it over the panel.

i put a bulletin board over mine.

Thank you! looks cute!