IKEA Ivar dresser - drawer does not fit

Do the strips only fit one way because of the drill holes? In a YouTube video, I was able to see the drawers; they are definitely built like mine. I can't say anything about the dresser, as I can't find any pictures.

I assume that you tried to insert the drawer from above. I would also say (also from experience, happened once and now always checked) that pages are often swapped or with IKEA furniture the upper or lower part is sometimes slightly misaligned. Or rails seem to be the same although they are not. (Does not have to be here now... If you don’t pay attention and check, you often end up with exactly the problem you’re facing now. My advice: disassembly and constant checking of the rail installation.

Passen die Leisten aufgrund der Bohrlöcher nicht nur auf eine Art?

No, often not. Try your luck again.

I have already installed the dresser; I can't get it out there by myself. Here are pictures of my moldings. Are they correct like this?

Or does the rail have to be on the left side with the L or the R? I did lay the boards on the floor as instructed, but maybe something got mixed up later during the further assembly.

I think that is swapped. The rails are labeled with L / R.

When I look at the instructions, the little wheels must be at the bottom of the body. In your case, they are on top. Edit: that would fit if you swapped L and R. So the mistake must be there.