This is what UptoDate, an online resource for doctors, says. You should read the whole article -- a lot of good info at the end: https://www.uptodate.com/contents/supplemental-oxygen-on-commercial-airlines-beyond-the-basics#:~:text=In general%2C airlines do not,rented through an oxygen supplier.
"In general, airlines do not provide medical oxygen, but allow passengers to bring a battery-powered portable oxygen concentrator (POC) for use in flight. POCs that are approved by the Federal Aviation Association (FAA) can be purchased or rented through an oxygen supplier. Approved POCs will have a label indicating that they meet FAA regulations. Airlines may require notification of the need for in-flight oxygen at least 48 hours before the trip, making it necessary to undergo testing at least three days before travel."
Here is a link to what TSA says, but it's really covered in the article: https://www.tsa.gov/travel/special-procedures