Decal image appears blurry / pixelated when placed

@Animation Guy, there is at least one other thread on this subject where I've posted several times and exchanged info with Adobe staff. There are apparently several threads on the forum that should be consolidated, but it is definitely not the case that the Stager team haven't responded. It's not a big team, and until recently it was a very small team.

The key to working around this issue is to match the external scaling of a graphic (in inches or centimeters) to what Stager thinks the scaling is. This works better than 95% of the time, in my experience. It's a workaround, not a fix, but that's not a show stopper (after all, there are large corporations using Stager for virtual photography and retail displays).

There's also Substance 3D Painter, which has a bit of a learning curve (he said, nonchalantly) but as far as materials and graphics are concerned, does everything Stager is capable of and a lot more.

What usually works is to use vector art that is the same size (as defined in the Illustrator file) as the model in the Stager scene. This seems to be because of how Stager interprets vector art on import. (I say "seems to be" because Jeanette tried to explain it to me once in an email, but it went over my head at about 20,000 feet, leaving a wispy contrail but not a lot of insight.)

In this demo, the box is approximately a 12-inch cube according to the Properties panel in Stager. In Illustrator, the helicopter graphic is about an inch square and the hiker graphic is 12 inches square to match the "size" of the model in Stager. They're both vector graphics, so any experienced designer would expect to scale infinitely. But they don't. The difference is obvious.

There is another workaround, which is to export the model's UVs, open in Photoshop and put your graphics there. It's not entirely satisfactory, because it doesn't allow for layered graphics with different properties (roughness, opacity, etc.), but it avoids the pixellation issue.

For reference, here is a post from way back in April.  Notice not one single Adobe employee even tried to address this problem.  See the thread here: https://community.adobe.com/t5/substance-3d-stager-bugs/imported-pngs-look-low-res/idi-p/13726255

I would encourage you to try it yourself.  You will be very discouraged with results.  This is a major bug which has been around since the first version of Stager, and has never been fixed by the Adobe engineers.  There are dozens and dozens of complaints about this on many forums, so this problems is very widespread.