What exactly is the question?

Oh yes, there was a long delay with this model because Optoma held back / recalled them for a FW update. That's why I convinced myself that the dust in the device might be caused by this and that the documents (warranty, manual) were not repacked during the recall (except for the batteries, only a large empty plastic bag). But there can't be that much fine dust and especially in the optics. But it is from an official agent and the box was sealed with Optoma glue.

P. S. Sorry, I wanted to reply for a long time, but I couldn't send the whole text, even though the length should fit.

Anyway, yesterday I had THE brilliant idea! A lot of things change in the optics when the focus is adjusted. So it could be that with a significantly different distance to the screen and thus a completely different focus setting, the light passes through the lens differently (angle, range), whereby the effects may become little or no longer visible... It gets better and worse with lens shift and probably also zoom...

I have problems with the picture display: blurring unevenly and depending on the operating temperature, edges in the lower corners seem to be outward instead of sharp. That's the worst. Otherwise a slight yellow discolouration in one corner. And I almost wouldn't care about the "stain" in the dark, you can't see it normally. Uneven illumination / colour representation is probably normal, but whether it is a bit too much for me...? The fact that the picture is not square but slightly curved towards the outside would also be largely irrelevant to me, especially if it is normal. Mind you, this is all with the test images, so external sources of error are (largely) excluded and I'm not stupid and it's not my first beamer.

The problem now is that the seller says that everything is completely normal, which (actually) can't be the case and that's why I'm in despair, as I'm firmly convinced that it's a technical defect (shift between chip and optics, dirt / defect in the optics - image is also not centred horizontally in the optics, which could explain various of these effects and there is no H-lens shift).
So what I'm looking for now is a way to examine a comparative device and hopefully see that everything is normal there while mine next to it shows the faults. That would be great! Otherwise I really don't know what to do... :( Everything can't be normal because it's a "cheap" beamer!