Fixed glazing plastic window is leaking

I’ll make it clear again for the gentlemen...

Then the "Montageleiste" is the glazing bead and the rubber seal lies against the glass. What is the temperature of the frame and how high is the humidity? Then you know if it is condensation.

But as @11ant writes, the picture is for the recycle bin,...

... and in my opinion prompts to a whole bag full of misinterpretations. You actually see NOTHING, but I would still interpret all points differently here. That is exactly the problem when questioners simply take pictures "as close as possible," DBDDHKP ...

Sorry, yes, I meant glass strip. For me it is very clear. What else could the dark thing be other than the window glass, from which everything else follows... You can even see the reflection in the glass. But sure, the best would be a better photo. High resolution, showing the entire window.

Well, then we know that nothing can be leaking.

Ok, here are a few more photos. I think Tolentino’s explanation was already quite good. This morning I applied the black tape to the joint between the frame and the mounting rail, leaving about 1cm uncovered. And exactly at this 1 cm, you can see a water droplet again, the rest is dry. If it were a cold bridge, wouldn’t there be condensation on the tape as well? By the way, it has been rain-free outside since this morning.