Parry is one of the core combat mechanics that you should be looking to master in Dragon Age The Veilguard. If you get the timing of your parry right on an enemy, you will be able to exploit them by forcing them to stagger and then leave them open to follow-up attacks.
However, it’s a high-risk, high-reward mechanic that will let you have a much easier time melting through bosses and other difficult content. However, the parry window in the RPG is tight and gets tighter on higher difficulty levels.
But once you can master the timing, you are going to be able to breeze through most bosses.
How to Parry in Dragon Age The Veilguard

To Parry in Dragon Age The Veilguard, you will need to tap the block button right before an enemy is about a land a hit on you. You will be able to pull this off as long as you have a shield, sword, or some other heavy weapon that will help you deflect the incoming attack.
By pressing Q on the keyboard or L1/LB on the controller to Defend or Block against an incoming attack. When an enemy attacks you will see a yellow marker flashing over their head, this indicates that it can be parried.
So tap the Block button right before the attack is about to land on Rook, and once you get the timing right, you will deflect the attack and catch the enemy off guard thereby stunning them.
However, do keep in mind that parry only works on attacks that have a yellow flashing mark on them. Moves that flash red cannot be blocked or parried and you will then need to use the Space key on the PC and O/B on controllers to dodge out of the way.
Parring takes a lot of time to master, but once you get the hang of the enemy patterns and their timings you will be able to breeze through most of the difficult encounters.
Note: You will be able to parry projectiles as long as you have a skill which allows you to do so.