I've hosted my own NuGet server, and it worked great for my libraries. In this case, I installed "NuGet.Server" package.
Recently, it doesn't work anymore and I can not push any version on it. When I've checked the issue, I found one of its dependencies which is "NuGet.Core", has been deprecated as it is legacy and is no longer maintained.
NuGet.Core
This package has been deprecated as it is legacy and is no longer maintained.
Additional Details
NuGet.Core is part of NuGet client v2 APIs. They have been replaced by NuGet client v3 and later APIs.
While installing "NuGet.Server" package, it still installing the deprecated package (NuGet.Core).
How do I host my own NuGet v3 server?
How to upgrade my existing NuGet servers to be v3 compatible?