Is this a proper way to deal with mold?

The window in one of the rooms in my rental apartment is old and has only single glazing. Mold is growing right above this window. After a brief investigation, it became clear to me that because the window is only single-glazed, it's colder in the window area than in the rest of the room in winter, causing moisture to accumulate and mold to form.

Unfortunately, the landlord sees things differently. First, they gave me a detailed explanation of how to properly ventilate. Then they came up with crude explanations, like the interior blind being to blame. After much back and forth, a company came by and started covering the area with some kind of insulation board, see picture.

I have the feeling the landlord just doesn't want to pay for a new window, but since I'm no expert, does the insulation panel option make sense? Is that how it's done? Won't mold continue to grow, just underneath the panel?