Memory allocation of Window 11 VM vs. Linux/Ubuntu VM

Well, I have two VMs configured with 64GB of RAM, one Windows 11 (24H2) and the other one being Ubuntu 24.04.

If I start up the Windows one, then MacOS (Sequoia 15.0.1 (24A348)) tells me that the memory consumption of this VM is about 64GB whereas within Windows itself almost none of it is consumed. Okay. Now if I start up the Ubuntu one, then MacOS tells me a usage of about 4GB despite also being configured with 64GB of RAM. Question is; why does the Windows VM allocates all the memory right from the start but the Linux one does not?