the Desktop one has 24GB the Low Power Mobile one Has 16GB i Will Explain it to you
the Mobile one in Laptops is 16 GB GDDR6 as it has a Memory Bus of 256 bit so has 8 x 2GB VRAM Chips to make it 16 GB (32 bits per chip)
the Desktop one is 24 GB GDDR6 as it has a Memory Bus of 384 bit so has 12 x 2GB VRAM Chips to make it 24 GB (32 bits per chip)
Mobile versions are not as powerful as a Desktop one as they massively Reduce the Power on them as there is not the Cooling (Would need to be 2 inches Thick) or Power Delivery to Power it unless you had like 3 DC power Jacks and Power Adapters that all had to be connected for it to even works that defeats it being mobile.
here is the data for each:
https://www.techpowerup.com/gpu-specs/rtx-a5000.c3748 <-- Desktop
https://www.techpowerup.com/gpu-specs/rtx-a5000-mobile.c3805 <-- Mobile