I use all sorts of things as headboard for clients; stained glass windows, old doors, iron Gates, wooden Gates or fencing, chair backs, architectural salvage yard stuff.....
Here are 25 ideas: https://www.thespruce.com/dreamy-and-totally-doable-diy-headboards-3017296
Contemporary ones can be a simple upholstered rectangle of foam on plywood using a modern fabric, leather or faux fur. Wood slabs look quite modern or made of wooden boards. Some even use wood flooring for their headboards. Then you can also cut squares of wood and stain, or upholster them and apply directly to the wall using a serated picture hanger on each or join altogether and use french cleat(s) to hang on the wall. https://www.youtube.com/watch?v=VEuUYCWfunA