Windows ISOs

https://massgrave.dev/windows_ltsc_links.html

https://massgrave.dev/genuine-installation-media.html

https://www.heidoc.net/joomla/technology-science/microsoft/67-microsoft-windows-and-office-iso-download-tool

https://rentry.org/fwt#links

https://tb.rg-adguard.net

https://docs.microsoft.com/en-us/deployoffice/overview-office-deployment-tool

Always verify SHA with 7zip for non-MS sources
SHA Databases:
https://www.heidoc.net/php/myvsdump.php
https://files.rg-adguard.net/category
https://msdn.rg-adguard.net/public.php
https://forums.mydigitallife.net/threads/mvs-dump.78070
https://dnhash.net
https://msdn.su

SHA Source for all of the above:
https://my.visualstudio.com

======= 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.