Regarding damage reduction calculation
This is a short documentation of how the damage reduction calculation was deduced based on testing in the Workshop. August 26, 2025 Patch confirms that armor and other damage reductions combined are capped at 50% total reduction, however it does not explain every detail, namely the order in which DR and armor are applied, how Zenyatta's Orb of Discord affects the reduction cap and the existence of a separate damage reduction buff cap. I will not provide images or videos, however whomever should be able to reproduce this with the mentioned heroes and abilities.
- 1. Armor reduction is applied after other damage reductions
Transformed Bastion takes 20% less damage due to 
Ironclad passive. Reinhardt's Hammer (100 damage) deals 73 damage. This is in line with Hammer damage being first reduced by 20% from 100 to 80 and then reduced by additional 7 from 80 to 73.
- 2. Combined damage reduction is not capped at 50%, combined damage taken modification is capped at -50%
Zenyatta's Orb of Discord applies a 25% damage taken amplification. This is additive with damage reductions, as hitting untransformed Bastion affected by 
Nano Boost (-50% taken) and Discord Orb with Zenyatta's primary fire (50 damage), will deal 37.5 damage to white health, which is a 25% reduction (-50% + 25% = -25% taken). (note: if you are using health numbers instead of workshop hooks to get the damage dealt, it may round to 37 or 38 instead)
This is more or less known already however, the more pressing question in light of the 50% cap is "Will armor reduction apply with Orb of Discord if the target already has 50% reduction from Nano Boost?" And the result of hitting Nano Boosted Bastion in the armored health, is that he takes 30.5 damage instead, which means that it does apply. This in turn shows that the 50% cap for "combined damage reduction" includes not only reductions but damage taken amplifications as well.
- 3. Damage reduction buffs are separately capped at 50%
The patch notes mention, how armor reduction is separately capped to 50%. A similar cap exists for damage taken reduction buffs. This also is kind of known, but I believe it needs to be explained to avoid confusion with this and the final cap being the same one.
Using Bastion as an example again, if damage taken reduction was only capped at the final stage, a transformed Bastion with Nano Boost and Discord Orb should receive -20% - 50% + 25% = -45% damage taken, or 27.5 damage to base health (and 25 to armor due to combined cap) from Zenyatta's primary. However, Bastion still receives 37.5 damage to base health (and 30.5 to armor) from Zenyatta's primary, which is the same as from the previous example with only Nano Boost and Discord. This suggests that the total of damage taken reduction buffs is also capped to 50% total before damage taken amplifications are added, meaning that there are three separate 50% limits, one for damage reduction buffs, one for armor reduction and a final one for combined damage taken modification.