$$damage = base \cdot (1 - accs) \cdot (1 - type - dr) \cdot \begin{cases} 1.1 & \text{if in Appeal Chance} \\ 1 & \text{otherwise} \end{cases}$$

$base$: Base Note Damage

$accs$: Sum of damage-reducing Accessory effects (Necklaces)

$type$: Gd-type bonus/penalty from active Strategy

$dr$: Sum of effects of active Damage Reduction skills

This formula is not correct, as it is missing the flooring. The order of multiplications needs to be investigated for that, but it is hard to do so as you can't see Stamina as a number in-game. One approach used by @devsifmatch in early investigations was to take screenshots before and after a note and use a script to calculate lost stamina by examining the area of the gauge that is still coloured. The smaller the max stamina of the formation, the more accurate this could be.