The latest tags for the dotnet/core repos are always intended to reference the latest supported version of .NET Core. At this time, the latest supported version is .NET Core 3.1. This version of .NET Core is also a long-term supported (LTS) release.
It is recommended to use a more-specific tag than latest for anything other than casual development. Once you have an application that you believe will eventually go to production, you are recommended to use a tag like 3.1.