The wooden slats have discolorations, is that okay?

I just received my wooden slats for the substructure of the rough plank. Unfortunately, they somehow look "shoddy." I checked by feel, and they all seem to be dry.

Probably the slats were partially somewhere damp…. I just looked at beetle wood but that looks completely different, still thanks for the tip

Quite certainly, this is not beetlewood, it really looks different. These are stain spots, basically fungal infestation, which does not yet damage the wood in the "dot" form. This occurs very quickly when freshly cut and sawn wood cannot dry. It happens when storing without spacers between the layers, especially outdoors. It usually appears on the sapwood, but can also spread from there to the heartwood.
In the visible area, as at home, you can remove it with mold and algae remover / washing soda / lime cleaner (alkaline, NOT ACIDIC!) and it will not come back as long as the wood is properly installed or stored. Structural limitations are not yet given in this form; I would not use it for living room paneling.