Your second output,
du -s Folder is in kilobytes not megabytes. That is the default output for
du. To convert to MB divide by 1024: 120664/1024 = 117.8359375, with the
h flag this gets rounded up to 118MB.
You can also view the size of the folder in Bytes with
du -sb Folder.
The du utility gives you the amount that is actually used by the disk. The value you are seeing in the file explorer is the apparent size. These are not the same as explained in
print apparent sizes, rather than disk usage; although the apparent size is usually smaller, it may be larger due
to holes in (`sparse') files, internal fragmentation, indirect blocks, and the like
If you use
--apparent-size option in
du it will give you the same value that you see in the file explorer.
As for why size on disk is different than the size of all the files, see this response: Why is disk usage greater than the size of all files on it?