Package Microsoft.AspNetCore.OpenApi 7.0.0 is not compatible with net70

I'm trying to set up a .net project.when I run dotnet build I get the following error:

C:\Projects\Map\Map\src\api\api.csproj : error NU1202: Package Microsoft.AspNetCore.OpenApi 7.0.0 is not compatible with net70 (.NETFramework,Version=v7.0) / win7 -x86. Package Microsoft.AspNetCore.OpenApi 7.0.0 supports: net7.0 (.NETCoreApp,Version=v7.0)C:\Projects\Map\Map\src> dotnet --version7.0.200

I downloaded and installed dotnet 7.0. What am I doing wrong?