I think I may have found the problem, but am not sure. I have 32 GB of Total RAM, but I have found that approximately half of the 32 GB of Total RAM (16 GB) is allocated to my GPU (Graphics Chip or Card). That leaves 16 GB for everything else (eg, allocated to me for my Apps). I'll call this "App RAM". So the percentage (%) that Task Manager's reports for Memory Usage % is based on how much of the App RAM is being used.
You can see how much of your Total RAM is allocated to your GPU on the Task Manager Performance Tab. Select the GPU, then look at the "GPU Memory" field at the bottom. Mine currently says: 2.0/15.8 GB (See Screenshot)
That means that the GPU is using 2.0 GB out of the 15.8 GB allocated to it (15.8 is approximately 16 GB). But nothing else on the PC can use the remaining 13.8 GB, because that's reserved for the GPU.
Some PCs allow you to change how much of the Total RAM is allocated to the GPU via an App on your PC or via an Advanced BIOS Setting, , but I haven't found a way to do that on my PC.
[Note: The RAM usage numbers still don't seem to add-up, because it says I'm using 22.4 GB of my Total RAM. If I were using all of the 16 GB allocated to App RAM and add the 2.1 GB being used by the GPU, that's a total of 18.1 GB in use. So I don't know what accounts for the missing 4.3 GB.]
