Run it as an administrator:
icacls "<path to the Magento's folder>\pub\media" /grant:r <your Windows name>:F /t
E.g.:
icacls "C:\work\clients\justuno\m2v\2.4.5-p1\j3\code\pub\media" /grant:r dmitry:F /t
learn.microsoft.com/en-us/windows-server/administration/windows-commands/icacls