When I last checked a half a year ago, there was no locking gas cap available for my 2019 E-450. You can buy a locking gas cap that will physically attach & lock, but I do not believe they are rated for the correct sealing vacuum. I have not checked locking gas cap availability for the F53, so I am guessing here.
If you still have the original gas cap, I would give that a try to see if the warning light goes away.
Please let us know how it goes.
2019 Minnie Winnie 22M on an E-450 frame