If you truly need a Windows environment or a recovery tool, here are legitimate options (none are 100MB, but they are safe).
Searching for a "highly compressed 100MB" Windows 10 ISO is a common starting point for many, but it is important to know that . windows 10 iso highly compressed 100mb
Even the most aggressive compression algorithms (like 7-Zip on Ultra settings) can only shrink a file by about 30-40% before it breaks. That would get you to roughly 2.5GB—not 100MB. If you truly need a Windows environment or
If you absolutely need a lightweight version for an old netbook, search for (by NTDev). Note: This is not official Microsoft software. windows 10 iso highly compressed 100mb