The Docker for mac GUI does not allow to configure less than
1GiB as allocated memory. In some cases you might want to configre a lower value, especially when you are limited to available RAM.
You can set any value in the config file. Just restart docker afterwards.
... "memoryMiB" : 1024, ...
Note that the final memory consumption might be higher than your configured value. So I guess, this covers only a memory pre-allocation, while the final consumption depends on you container setup.