If they’re Luan (economy mahogany) then they’ll be a bit porous.
If you want to paint or stencil or appliqué somethings on them, you may need to put a paintable sealer on them to deal with the porosity.
You can paint. I would suggest taking them down and use a paint sprayer outside. Clean with TSP than sand off sheen. Prime with oil based primer and paint with oil based paint.
Carol I once redid my closet doors for the holidays. I placed photos and cards in the slats. Then I used ribbons through the slats after the holidays.
It took a lot of work but the ribbons stayed there for years.
I hope this gives some inspiration.
I turned mine into "french" doors that opened in the center. I read a ton of tutorials before starting. I sealed the stained wood with Kilz after scrubbing them and then painted them a beautiful pastel color.
Here's a roundup of 10 Bifold Door Makeover Ideas: https://www.brightgreendoor.com/diy-bi-fold-closet-door-makeovers/
Here are some ideas you might be interested in....