A320 Flight Attendant reported being notified after arriving at destination that a passenger packed a prohibited personal oxygen machine in checked baggage.

Narrative

When we landed back in ZZZ from ZZZ1; the LFA (Lead Flight Attendant) told us that we had a huge risk on our flight that we didn't know about until we have deplaned. They said they saw a personal oxygen machine that you plug into the wall at home being brought up for our passenger who was deplaning in ZZZ and LFA asked what is that and where did it come from. Apparently it was checked in and was with the baggage under the plane from my understanding; the way the LFA explained it to us all. I never got to see it because I was in the back of the plane and by the time I made it to the front; all passengers had deplaned.From my understanding; personal oxygen is not allowed to be brought on the plane and kept on person or be checked in. This is a very serious matter and needs to be looked into before this passenger tries to travel back with it on the next flight or if someone else brings it and employees don't follow the safety protocols/rules. It's a disaster waiting to happen in the air. Train ticket counter agents; gate agents; and bag loaders to not accept personal oxygen systems to be loaded under the plane with the luggage to prevent aircraft fire/explosion.