[2023] Supreme Grandstanding (2 player) Theorycraft

Ok so the text of Supreme Grandstanding says that any charge is shared amongst allies

It says allies share their charges (of any type) with you, not the other way around. Sharing is not innately bidirectional. If entity A shares charges with entity B, that means when A gains a charge, B will also gain a charge. This requires that both of them can gain that kind of charge.

If B has 0 maximum charges of that type, B cannot gain the shared charge.

Charges are not buffs, and do not innately apply any bonus to players (or monsters). If B does not have any stats which give them something for having those charges, any such charges they gain will do nothing for them.

So if both players have Instruments of Zeal, then one of them could usefully share Fanatic Charges with the other.

All characters innately have specific bonuses-per-charge for the three standard charge types, and the three "alternate" charge types they can be effectively replaced with by the unique belts. These can be seen in the character panel so long as you have the ability to have charges of that type.

Player B did not gain an Endurance Charge, so cannot share one. They gained a Brutal Charge.

Player A, without the belt, has 0 maximum Brutal Charges, so cannot gain the charge B tried to share with them.

But if Player A gains an Endurance Charge and shares that with B, B will gain a Brutal Charge instead due to the belt's effect.