https://www.ch-aviation.com/orders has data on which airlines will receive which planes when

ch-aviation

Most extensive and up to date airline knowledge base: More than 50,000 aircraft, 6,500 airports and 5,000 airlines, access to fleet lists, worldwide airline schedules and route networks, airline management contacts, airline capacity and frequency analysis, airline PSS directory, up to date airline and route network news.

For context, Frontier Airlines' parent company Indigo Partners has ordered 32 A321XLR planes, with Frontier to receive 18 of them, scheduled for delivery in Q2 2024. However, the plane's delivery date has been pushed back, originally planned for late 2023. The A321XLR completed its first transatlantic passenger test flight in Oct 9 2023.

Furthermore, Frontier hasn't definitively stated whether or not it will fly to Europe:

The A321XLR “will enable us to fly to Europe, Hawaii and deeper into South America,” Frontier CEO Barry Biffle told the Routes World 2022 conference in Las Vegas this week.

Flying transatlantic is “definitely in consideration,” he added.

https://aviationweek.com/air-transport/airports-networks/frontier-airlines-ceo-transatlantic-a321xlr-routes-definitely

Frontier would only be able to fly between the northeastern US and Europe. Its parent company also owns Wizz Air, a European low-cost carrier.

Notably, the aircraft's range would likely fall well under the certified maximum if Frontier fills it with 240 seats. The airline would also need to figure out a way to allow for a lie-flat crew rest area for pilots on longer flights.

https://thepointsguy.com/news/frontier-airlines-europe-barry-biffle-interview-a321xlr/

@ampdot Can I put this in the question description?

@Tetraspace yeah!