How do I support both .Net 6 and .Net Framwork 4.7.2 with my nuget package

I'm creating a class library project that is packaged to Nuget.org (NugetGithub). Right now when I create the nuget package the only runtime it supports is .Net 6.

I need it to also support .Net Framework 4.7.2 as well for use in a WinForms application.

How do I fix this?