If you intend to buy a 5G smartphone that works on the M1 5G network, the following models will work :
M1 just added the Samsung Galaxy S21 series, OnePlus 8T, Oppo FInd X2 Pro 5G and VIVO X50E 5G.
Samsung Galaxy Note20 5G, Samsung Galaxy Note20 Ultra 5G, Samsung Z Galaxy Fold2 5G, Galaxy S20 FE, Galaxy A42 5G, Huawei P40 Pro 5G, Mi 10T/10T Pro 5G, iPhone 12 series (12, 12 Pro, Mini & Pro Max), Huawei Mate 40 Pro 5G, Oneplus 8T 5G, Oppo Find X2 Pro 5G, VIVO X50E 5G and Samsung Galaxy S21 series (S21, S21+ & Ultra 5G).
Other than the Samsung which are indicated as supporting the future Standalone network, the status of the other devices are unclear.