That is a very very new aircraft. The notes on the jetphotos.com posting (photo taken 2/21/2021, uploaded 2/27/2021) say:
the first A321neo for jetBlue with the Mint suites on board for North American flying and the new "Ribbons" tail design...delivered 26.02.2021 as N2501J
Delivered only yesterday!
The N-number must be a typo, because N2501J is registered as a Cessna 150 and that registration doesn't expire until August 2022. Happily the posting tells us the manufacturer's serial number, 10101, and the FAA's N-number lookup tool allows a search-by-serial among other options. We see that JetBlue is the proud new owner of MSN 10101 N2105J, recently arrived in New York. I don't know when the stickers removal takes place but I suspect it happened before the aircraft left Germany.
Zoom in and contrast/brightness adjusted to reveal N2105J underneath the sticker
The general idea is that the German registration is only temporary until the aircraft is re-registered under its new owner. In fact looking at all jetphotos.com entries for D-AZAJ we can see that specific registration seems to be a relatively common one for fresh-off-the-line A321s: June 2009 in US Airways livery, February 2013 Turkish Airlines, August 2013 Air China, April 2019 Air Transat, December 2019 Starlux, February 2021 JetBlue—all different serial numbers.