What to use to stencil/decoupage / or paint my boring old freezer?

Ooh, it sounds like a fun project! if the freezer is the kind with enamel coating - clean well, lightly sand use paint for metal and have fun!

You could "wrap" it with sheets of stainless steel. Many colors and finishes to choose from. Amazon is a good source. Don't forget to order 10% more than you actually need, for mistakes, etc. And, yes, you could paint it too. Be sure to get paint made especially for appliances. Best of luck to you.

You can successfully spray paint a fridge or freezer with a metal paint. Make sure there are no lit pilot lights near by.

There are decals sold for appliances.

https://www.vinyldisorder.com/appliance-decals-refrigerator-decals.html

https://applianceart.com/product-category/appliance/refrigerator/

https://www.amazon.com/slp/decals-for-appliances/9m4myc668hck65e

https://www.wayfair.com/keyword.php?keyword=appliance+decals&curpage=2

https://www.bestapplianceskins.com/

https://www.tenstickers-canada.com/ideal-for/appliances/

It’s fairly easy to redo an old freezer. First unplug it and check the pigtail for frays, outdated plug, or other problems. Check the drainage plug and any coils under or behind the freezer.

If you haven’t already emptied the freezer, I suggest you do so, tossing outdated food as you go. Drain and dry any moisture from inside the freezer, and check the rubber seals. If you see any rusty spots inside, spray them with Kilz or Rustoleum. Place an upended bag of charcoal inside to absorb any odors. Clean the inside of the freezer, too.

For the outside, sand the surfaces. Paint over rusted areas with Kilz or Rustoleum. You can paint the entire freezer with these paints as a base/primer coat, or use another paint for a primer, at least two coats.

Creative finishes: paint stripes or other geometric shapes. Cover with contact paper. Use stencils or blocks for designs. Decoupage large pictures from magazines, photos or a printer. Decoupage wrapping paper. Go crazy with Unicorn SPiT. Add lace or paper borders. Do real or fake family handprints. Add sparkle with glitter or gems. Add shiplap to the sides. When you finish decorating, seal with a couple of coats of polyurethane.

And PLEASE document and post on Hometalk. I can’t wait to see what you do! ☺️