Good news — the Apple iPad Pro 12.9-inch (6th generation) supports eSIM, so you can install a data plan without a physical SIM card.
Go to Settings → General → About. If "Available SIM" or a similar eSIM label appears, your iPad supports eSIM.
Some carrier and region variants of this device may not support eSIM, including versions sold with a physical dual-SIM tray in certain markets. Always confirm on the device itself using the steps above.
