Does this part need to be stuck down all round? It’s bonded on the drivers side only and slightly raised on the other ? Any ideas? (Or even why it’s there?)

Could it be a cover for the wiper mounting point for LHD vehicles?

The wiper spindle would not be central.

 

Looks like a bodge, as if someone has cut the trim panel in half to remove it or replace it easier and glued an overlapping fillet onto one half, I doubt that VAG would do that but nothing surprises me these days.

 

In any case if my theory is correct it would only be bonded to one side to allow removal.

Based on my mk1 Octy, I think it's a split in the panel to allow access to the pollen filter without the need to remove the wiper arms.

I’ve noticed this on 2019 and 2020 Octavias and Fabias as it happens....