No clue, but just a tip - I have a glass container specifically for onions that are cut, I always keep it in the fridge; since it's onions-only in that container, doesn't matter that the lid has an odor, and it keeps the onion smell out of the rest of the fridge. So, you just do that -- make it your onions-only jar.

I would try putting it outside in the sun. It worked for the silicone ring from my Instant Pot.

Thanks for all the responses. I will give them each a try: lemon juice, vinegar and sunshine. mxk3: That would be a good idea, but this didn't do a very good job of keeping the smell contained.

^^ Hmm, I wonder if perhaps the lid doesn't fit tightly enough or perhaps you didn't snap it firmly shut. You can pick up a new one inexpensively at places like TJMaxx.