MacBook pro,2016,16 GB RAM, Mojave 10.14.1,Parallels 14.1.0 500 GB Diskspace, 250 Reserved for Parallels/Windows 10 My Mac Shows me: 64 GB Parallels, 9 GB ICloud Drive,6 GB documents, 5 GB programs,3.5 GB div.,3 GB IOS, free Space 12 GB !!, System 394 GB!!!! On Windows 10 „Hard" Drive C has a capacity of 255 GB, used 58 GB, free Space 196 GB 394 - 256 = 138 GB used by System of Mac??
If Mac shows 64GB Parallels, then it is what Parallels takes. Strange numbers of free / system space are likely a purgeable space. We saw it several times on computers in our company. https://support.apple.com/en-us/HT202867