Beginning of Schimmel?

Hello,

I noticed this morning this:

[https://ibb.co/GxKNSbz](https://ibb.co/GxKNSbz)

And I wanted to ask please if it is the beginning of Schimmel. So far, I have been airing the apartment 3/4 times a day. Heating for 3/4 hours at night as I didn´t feel it was too cold during the day.

Any advice how to proceed if it is indeed Schimmel please?

Thank you in advance!