How can I use expired oatmeal?

You can feed it to the birds

Facial and body scrub? https://www.scratchmommy.com/diy-sugar-exfoliating-facial-scrub/

Use it in dough for children's sculpture or ornaments.

Birds love it!

You can make a soothing heat pillow that can be microwaved to heat and put on aching muscles. Just used the same recipe that uses rice, but substitute the oatmeal. Here's a tutorial for the rice.

https://www.onegoodthingbyjillee.com/homemade-heating-pad

it's a dried grain doesn't go bad easily.It lasts for years. https://www.eatbydate.com/grains/cereal/how-long-does-oatmeal-last-shelf-life-expiration-date-storage/ You can use to make soap,put in cheesecloth bags added to hot bathtub as moisturizer,feed to live stock,birds,add to compost great in garden.

Use it as a base for bath soaks

https://craftinvaders.co.uk/home-made-bath-tea-bags/