Filename: en-us_windows_10_iot_enterprise_ltsc_2021_x64_dvd_257ad90f.iso

https://massgrave.dev/windows_ltsc_links.html

https://pixeldrain.com/u/6y73DJZ2

https://www.heidoc.net/php/myvsdump.php SHA database
Always verify SHA with 7zip for non-MS sources

IF ALL LINKS ARE DOWN:
You can google the SHA-256 hash below and download it from anywhere, then verify the SHA-256 with 7zip to make sure it hasn't been tampered with.

Details: https://www.heidoc.net/php/myvsdump_details.php?id=p8166f112307ax64len
SHA-256: A0334F31EA7A3E6932B9AD7206608248F0BD40698BFB8FC65F14FC5E4976C160

======= Verify SHA-256 with 7zip =======
https://www.7-zip.org/download.html
Install 7zip > right click ISO > CRC SHA > SHA-256
If the SHA-256 matches the one from visualstudio.com, then the file has not been tampered with since its official release.