Are these indoor or outdoor?
If you are talking about the ones on a wall, II use Command strips to hang a piece of art over mine.
If they are indoors, here's a cute idea: https://www.hometalk.com/14498250/repurposed-kitchen-cabinet-door-covers-ugly-fuse-box
A full length mirror can cover it. Usually they are similar width to the utility boxes. Hopefully the box is flat against the wall that you can do this.
A piece of artwork larger than the utility box works great or depending upon where it is you might cover with pretty paper or use as a magnet board if it is metal like mine.
You could do something like this: https://thecarpentersdaughter.co.uk/diy/diy-radiator-cover/
We had one on our enclosed back porch that I would attach a big summer hat in the summer. Baskets work, too. Command strips make it easy. If you are talking outside, be aware that the utility company has the right, legally to remove anything that limits their access. My husband retired from an electric utility, and I have heard some sad stories about landscape being removed, shrubs cut, etc. If you paint a box the same color as your house it will blend in, and shrubs placed away from the box can camouflage without obstructing. Good luck and stay safe!
Here is an idea for an outdoor one:
For safety sake, use Command hooks to hang a picture on top of your utility box. The lines coming to the utility box come from above the box. Don't try a nail or screw to hang the picture because you might hit one of those lines.
I would put a wooden trellis and a climbing plant in a planter in front of the box, This way the plant could be moved.
You did not specify if you are referring to a meter outside or a fuse panel inside. Two completely different ideas.
Contact paper would be my go to answer on this question.
You could use a strong cardboard box and pop it over once decorated to match the room, or make up a timber frame and apply thin MDF to it - decorate and pop that over, or build a cupboard around them. Good luck!
Are you allowed to cover? there is probably an easement.