ok I think I see your problem. You have a cluster size of 2MB, usually this shpould be 4kB for NTFS (for disks smaller than 16TB).
This means that each file at minimum requires 2MB of disk space even it is smaller in reality. For example, a 10 kB file would eat up 2MB on disk, and a file with 2,10MB byte would eat up 4MB of real disk space. Since MSFS consits of a lot of files (and small ones for that matter) this can add a huge amount of unneccessary occupied disk space.
for reference: https://support.microsoft.com/en-us/topic/default-cluster-size-for-ntfs-fat-and-exfat-9772e6f1-e31a-00d7-e18f-73169155af95
By any chance: what make and model is the SSD you have installed MSFS on?