I have noticed that when I get the viewport/camera so close to the hair, it starts showing up.

It's unfortunate really, because my project is 24fps and I'm using the anti-alias workflow from William Faucher's YouTube MRQ video (from awhile back). Also, unfortunate because this isn't mentioned on Reallusion's page dedicated to tweaking settings for UE5:

Character Creator to Unreal Engine 5 Best Practice - Reallusion Magazine

The Kevin model looks great in the demo videos, but I've had less luck with a different character and hairstyle. For this project, I have moved on to Groom assets created in Blender and exported/imported as Alembic files.

The 30fps I mentioned was just a ballpark number. If you have static camera with people in front of it then you might not see artefacts. If you have a static camera and people driving by in a fast car you might encounter them.
This is a good writeup from Epic staff:
https://dev.epicgames.com/community/learning/tutorials/GxdV/unreal-engine-demystifying-sampling-in-movie-render-queue
Note that he recommends odd number of temporal samples (Faucher used even number of temporal samples).


I also think that Alembic groom is the way to go for UE5 users. It's the foundation of MetaHuman hair and should have a good out-of-the box support.
Unfortunately I haven't found a large collection of good looking premade groom hairstyles for Blender. Does that exist?

I also have a hard time to create black hair. All the hair models I tried come with brownish hair and when I reduce the base color multiplier in the Unreal shader a lot of red color artefacts appear.
So looks like I am tweaking the wrong parameter here.

The asset I used is a good start and allows you to customize as necessary. I exported the model from UE5, brought it into Blender and then used the assets for the hair, beard and brows. Example below. Note that any issues are related to my technical deficiencies and not the product itself.



I'm not affiliated with the asset's creator and am not receiving any consideration, but if you're interested learning more, link below:

Blender Facial Hair Toolkit (gumroad.com)

Have you tried playing around with the "alpha power" in Unreal Material Editor ?

Yes.

you weren't satisfied with the results though ?

I'm still trying to figure out what's wrong. In UE5, this is a screen snip of the hair materials. Note the jagged appearance of the transparencies. Is this how it's supposed to look? tx

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I don't believe that the thumbnails are entirely indicative of the way the material should look in the viewport. Lighting and Engine Scalability settings play a bigger part in how the materials will look.