Unknown Source Using 500 MB: Identifying Memory Usage on Linux Mint XFCE

I switched from Windows to Linux Mint XFCE and am currently checking and testing it. I used htop to monitor my usage and noticed many tasks running. My memory usage is being used around 522 MB, but there are about 15 tasks using memory ranging from 2.8 MB to 1.1 MB each, which adds up to roughly 20-30 MB. I can't find what process is using the remaining 500 MB of memory. Can anyone help me identify where this memory is being used?

Screenshots:
https://imgur.com/XJLUWW9.png
https://imgur.com/RHWhS4J.png