Windows 10 shows inconsistent folder sizes, what is the cause?

I just bought a laptop that has Windows 10 pre-installed and I would like to use dual-boot Linux. To this end, I am trying to verify how much disk space Windows uses in order to decide which partition to assign. I find it ridiculously difficult to get a definitive answer to something so simple. I have not used Windows for a while, so maybe I'm not understanding something.

If I click with the right button on the C: drive in the File Explorer and select Properties, I use the disk: approximately 41 GB.

However, if I download the du utility from sysinternals and run it on the C: drive, it reports 23,134,749,584 bytes on the disk, that's about 21.5GB. Why does File Explorer report almost twice this number? As far as I know, du shows hidden folders in your summary. Is there something else missing?

Also, if I go back to the File Explorer and right click on each individual folder on the C: drive and see its individual Properties, its sizes are added to something that matches the du report (that is, about 21 GB , not 41 GB).

Therefore, I can not make the reported disk usage of File Explorer on the C: drive agree with anything else I can see. At the same time, it is the largest number and I do not want to discard it in case the other tools do not have a "real" use.

Can someone help me explain the discrepancy?