Hi @cj2024,
Firstly, welcome to the Bunnings Workshop community.
It's a unique style of drain that I haven't been able to find any information on. Have you tried sticking a flat head screwdriver down through the hole and levering the middle up? If there is obvious movement, it is likely just a clip in piece that will pop out with some pressure.
If this doesn't work, you may have to clean it in situ. I suggest using a Ramset 20mm x 300mm Hole Cleaning Brush alongside CLR.
Let me know if you need further assistance.
Jacob
