AW3821DW, is it normal to have one dead pixel?

No certainly it's not common 

Total 6+ dead pixel qualifies you for another replacement 

I would say keep testing for a week or 2 

You might want to check out the DELL policy regarding this:

DELL display Pixel Guidelines 

For your warranty, it is best to discuss that with a DELL agent, as they are best suited to address warranty questions.

I should add to this that this is not an uncommon issue, and is related to the manufacturing process of the panel. This is something I always dread when purchasing a new LCD monitor, because I know there's a certain change of having a dead or stuck pixel. It's the main reason why I only purchase monitors that have a different policy, and guarantee no dead or stuck pixels. It's not cheap, but worth it in my opinion because even 1 pixel that catches my eye will always catch my eye once I notice it.

I did read the DELL display Pixel Guideline and have received a replacement unit yesterday.

The replacement unit has no dark spot but 1 dead pixel was found.

I plan on keeping it because it is better than my first unit which has 1 dead pixel and a dark spot.

Considering this is a high-end monitor. I just want to know is 100% no dead pixel panel is hard to come by.

 @Larcade 

Run Deadpix portable to try and unstick the deadpixel

https://codedead.com/software/deadpix/

https://codedead.com/Software/DeadPix/DP_Port.zip

Big thanks, trying it now

I am one of those people, lol. But I only buy monitors with 100% no dead/stuck pixel warranty.

I have been running deadpix for hours. It didn't fix it.

Guess I'll have to settle with 99.9% lol

@Larcade  I really appreciate users Like you, most  KARENS would ask for a replacement because there is scratch they can not live with, 

Less E-WASTE