Do I need to drain my iPad Air M2 before first charge?

Expanding upon stedman1’s sage advice...

Unlike some older battery chemistries (that may suffer "memory" effects that might restrict a battery's ability to charge), there is no benefit whatsoever to be had in fully discharging a Li-ion battery.

You should never intentionally fully discharge a Li-ion battery - as, if allowed to remain in this state (unintentionally or otherwise), the battery can suffer permanent and irreversible damage.

While occasional full discharge will cause no harm if immediately recharged, you would be well advised to aim to routinely keep your iPad battery above 20%. This safeguard helps to avoid the possibility of forgetting to recharge your battery before state of battery charge becomes critical. While your iPad should automatically shut-down prior to fully discharging its battery, unless immediately recharged, the battery can fall into a state of deep discharge from which it cannot recover.

No. There is no requirement to drain modern lithium based batteries. Repeatedly doing so will shorten their lifespan.