Help cleaning Geberit turncontrol drain

I’m trying to clean the drain on the bathtub, but I’m not sure how to detach it, mainly I’m not quite sure what is the model.

It looks a lot like Geberit 151.550, but it’s a little bit different. I got the manual on Geberit site, and I could remove the plastic cover, but the screw is very different (it should be a PH 2, but instead looks like a regular screw). I tried to turn it and it was impossible at the point I had some doubts if this is really a screw (photo included below). The daisy-like cover is different too, so I’m clueless (photo also below).

Do you know how can I detach it?

Thank you!

Daisy-like cover:

Detail of the screw inside: