The Intel NUC 13 Arena Canyon mixes M.2 2280 and 2242 slots

The Intel NUC 13 Arena Canyon uses two different M.2 sizes — a full-length 2280 for the primary PCIe Gen 4 x4 NVMe drive, and a shorter 2242 for the secondary Gen 3 x4 slot. There’s no 2.5-inch bay at all, so everything is NVMe. The mixed slot sizes mean you’ll want a 2242 drive for the second position rather than assuming both take 2280.