Start with the simple checks: verify your internet connection, run the Windows Update troubleshooter, and clear the SoftwareDistribution folder. If those don't help, move to the more targeted fixes: adjust Group Policy settings, run DISM and SFC scans, or manually install the update using an ISO file or the Microsoft Update Catalog. In the rare case that nothing works, an in-place upgrade will restore your system to full health.
: Attempting to install these features while on a restricted VPN can block the necessary handshakes with Microsoft's content delivery networks. Strategic Solutions
Active proxies and overprotective third-party antivirus firewalls can block the network handshake required to download optional components.
dism /online /enable-feature /featurename:NetFx3 /Source:C:\sxs /LimitAccess
Are you attempting this on a or a work-managed computer ? This will help determine if a Group Policy is likely the culprit.