Net Framework — 3.5 Sp1 Offline Installer |link|

.NET 3.5 SP1 is by Microsoft as part of the lifecycle for Windows Server and Windows 10/11. Security updates for .NET 3.5 SP1 are delivered through Windows Update monthly (Patch Tuesday). Ensure you have the latest updates after installation.

Option B — Silent/unattended install (useful for scripts or many machines) net framework 3.5 sp1 offline installer