If you need a modern OS on extremely old hardware (512 MB RAM, 4 GB disk), Linux is more realistic:

Instead of chasing a dangerous 100 MB file, follow this safe method to pare down a legitimate Windows 10:

: You can achieve a 1.2–1.5 GB compressed ISO, which expands to ~3.5–4 GB on disk. Still far larger than 100 MB, but functional and clean.

Are you looking to install this on an older computer with low RAM, or are you just trying to save space on a download?