How do I enable the NuGet Package source Type on creating Local/Remote/Virtual Repository?
I have installed JFROG Artifactory OSS version(7.35.2) and when I'm trying to create Local/Remote/Virtual Repositories for NuGet, but I can't able to choose NuGet from package source type. FYR attached screenshot.

If this option is not available with Artifactory OSS version, then suggest the way to do upload/downloading NuGet Packages with JFrog.
And forget to update, when I have tried with JFrog Cloud version, there I can able to use NuGet package Source Type.
Artifactory OSS supports Maven, Gradle, Ivy, SBT, Generic package types as per this confluence page and hence you are not able to view Nuget options in OSS.
You might have tried JFrog cloud Pro version where it comes with license and you will be able to view all package types. You will need a minimum Pro license to use the Nuget package type.