I just discovered a very interesting thing that proves that the limiting the battery charge threashold to 2024 iPads is just an arbitrary choice by Apple (that could probably fit into the planned obsolence strategy for older devices).
At some point in either iPadOS 16 or 17 (probably with the introduction of Stage Manager) Apple made a change that keeps the charge level stable when connected to an external monitor that charges the iPad.
This does not work on iPadOS 15 but works on M series and A12X, even without enabling stage manager.
It's great as it allows to have the iPad plugged to a monitor all day without keeping it at 100% during this time (or quickly discharging it in the case of portable monitors).
At some point in either iPadOS 16 or 17 (probably with the introduction of Stage Manager) Apple made a change that keeps the charge level stable when connected to an external monitor that charges the iPad.
This does not work on iPadOS 15 but works on M series and A12X, even without enabling stage manager.
It's great as it allows to have the iPad plugged to a monitor all day without keeping it at 100% during this time (or quickly discharging it in the case of portable monitors).