The only exception to that is if you purchase the iPad on contract with ATT Next its locked to ATT, It can be unlocked but you have to use a Sim card. ESIM is disabled on them.
That one's carrier "locked" to begin with anyway (more like carrier visibility/reveal rules). Apple Embedded SIM and eSIM work but can only be used with AT&T (should actually be setup with the iPad line when you receive it).
The Nano SIM slot is technically unlocked but if using another carrier, it has to be activated already before installing on the iPad as the same carrier visibility/reveal rules apply.