Shower drain too high, water does not drain, silicone is peeling off

In the second picture you can see that the front joint is sticking up a bit.

No, that's nothing. Or I don't see your second joint.

Does it just look like that, or is the small tile on the far left not properly grouted?

Basically, a small incision is enough for the drainage of the residual water, right where the water stands at the "lowest" point at the gutter? The risk of damage is lower there - especially since you could almost "Dremel" it microsurgically and see if it helps?

But the sheet metal there is only very thin. I wouldn't do anything at the gutter. For me, only the suggestion from Haas-handwerk would be an option. Remove and correctly reinstall. Especially since the quality of the grouting is very poor anyway. Are the black spots mold? I wouldn't be surprised.