Weird top-right hole on A1 heat bed

I thought that hole should be the same with other 3, but this hole is not for screws, and it contains a lot of metal dust (not attractive to magnet so I dont know what it is). Is this normal?

here is the video: 20240513_205549.mp4 - Google Drive
it would be great if someone can share the image of the heat bed so I can take as reference to check

Yes, this is normal. I was a bit astonished too, when I got my A1 as it differs from the A1 Mini here (which has 4 screws).
If you run Manual Bed Tramming, you will notice that this corner is left out as there is no screw.
So, 3 screws seem to be sufficient to level the bed.
The debris you mentioned can only be left over from manufacturing process as there is no way it would get there from the printer.

That would be aluminum since that’s what the heat beds are stamped /or milled out of.

Looks to be a hole for fixturing when they machine the bed, maybe an alignment dot the use when lasering the part which is typically referred to as a [Tooling Hole] or [Locating Hole]