12+12GB doesn't result in a power of 2. 8+24GB does, but there are no 24GB DDR4 SODIMMs to make it with, so that's only possible with DDR5. Moreover, even though that is possible, you can then look at the specs to confirm that it isn't the case, having already filtered out all of the junk where it clearly is the case, e.g. when the machine has 40GB.