Because 1607 is over 8 years old, the Windows Update agent will try to download hundreds of cumulative updates, driver updates, and definition updates sequentially. This can take 12 to 24 hours.
This is the million-dollar question.
Microsoft released a "Convenience Rollup" for 1607 (KB3213986). You should download this standalone package from the Microsoft Update Catalog (on a modern PC) and side-load it onto your 1607 machine. Windows 10 1607 Iso Download 64 Bit
If you downloaded a standard "Windows 10 Pro 1607 ISO," keep that PC air-gapped (no internet). If you need internet, upgrade to Windows 10 22H2 or Windows 11. Because 1607 is over 8 years old, the
