iPad Air 4th generation cannot set battery charging limit

As illustrated by sberman, your iPad Air 4 does not support the charging limit feature.

While the option to a set a charging limit is only available to newer models of iPad, independent studies have shown that for an iPad that is in regular usage, there is very little if any benefit in restricting charging to below 100%. For devices in regular use, limiting charging to 80% simply shortens battery autonomy before the device must be recharged or used while connected to external power.

Storing a Li-ion battery at 100% charge for extended periods can be detrimental to long-term battery health - potentially reducing the health and performance of the battery over its operational lifetime. For iPad's in regular use, the difference in battery lifespan has been demonstrated to be negligible - any recordable performance differences being within the margin of measurement error and inherent differences between individual batteries. If you plan to regularly store your iPad for long periods, simply avoid storing it with a full charge. Occasional extended storage with a full charge is unlikely to cause any issue whatsoever.

What will significantly shorten the lifespan of a Li-ion battery is allowing a nearly discharged battery to remain in this state unnecessarily - or setting aside a fully battery for any length of time. In this state the battery can enter a state of deep-discharge, this being a condition from which the battery may never recover. Always recharge your iPad battery when low; never set aside, without recharging, if the iPad shuts-down due to low battery.

That is correct.

There’s no reason to set your battery limit. It is an old wise tail.

I think you meant to say wives tail.