Many thanks for the information - unfortunately this only answers my question to a limited extent.
I know that 8-core GPU models are more expensive, but I still don't know how many "cores" the GPU has in which model and also not specifically in the device I selected.

Macbook Air (2020) with M1 processor:
The base model offered with 256GB SSD has 7 GPU cores.
The basic model which is offered with 512GB SSD has 8 GPU cores.
But since there are also upgrade models, only the manufacturer can say that. Digitec would have to state this in the specs. All other dealers do the same.
Otherwise you can find out by comparing the prices. 8-core GPUs are more expensive.