Chiming in here to confirm that this is correct. The official 5.0 release included new dependencies on DirectX12’s Agility SDK for Nanite and your PC must absolutely have the latest version of Windows (version 1909+) and latest GPU drivers. Vulkan will also work.
For old Preview projects, you may need to migrate the content to a new project or otherwise delete the DerivedDataCache and any Intermediate / Saved / Binaries. DirectX12 must be the RHI for the project.
For users of Windows Server 2019, Windows version 1909 is not available and you should upgrade to Windows Server 2022 as soon as possible. In the meantime, when all else fails there is a console variable r.Nanite.RequireDX12 that can be placed in BaseEngine.ini / Engine.RendererSettings / r.Nanite.RequireDX12=0. This loophole will be closed with the 5.1 release and should not be relied on.