Does global.json specify sdk in Asp .Net core 5.x?

This article explains the policies used by the .NET Core tools, SDK, and runtime for selecting versions.

Error Message:

cd /src/Presentation/Nop.WebSeoForMobile
root@iZuf:/src/Presentation/Nop.WebSeoForMobile# dotnet run
/usr/share/dotnet/sdk/3.1.301/Microsoft.Common.CurrentVersion.targets(1177,5): error MSB3644: The reference assemblies for .NETFramework,Version=v5.0 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks [/src/Presentation/Nop.WebSeoForMobile/Nop.WebSeoForMobile.csproj]

The build failed. Fix the build errors and run again.

step 1:Check everything installed correctly

To make sure it works after you’ve set it up, just run:

# dotnet --info

output

.NET Core SDK (reflecting any global.json):
 Version:   3.1.301
 Commit:    7feb845744

Runtime Environment:
 OS Name:     ubuntu
 OS Version:  18.04
 OS Platform: Linux
 RID:         ubuntu.18.04-x64
 Base Path:   /usr/share/dotnet/sdk/3.1.301/

Host (useful for support):
  Version: 5.0.0-rc.1.20451.14
  Commit:  38017c3935

.NET SDKs installed:
  3.0.100 [/usr/share/dotnet/sdk]
  3.1.301 [/usr/share/dotnet/sdk]
  5.0.100-rc.1.20452.10 [/usr/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 3.0.0 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.5 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.0-rc.1.20451.17 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.0.0 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.5 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.0-rc.1.20451.14 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

step 2:Select one of the .NET Core versions from .NET SDKs installed 

version selected

.NET SDKs installed:
  3.0.100 [/usr/share/dotnet/sdk]
  3.1.301 [/usr/share/dotnet/sdk]
  5.0.100-rc.1.20452.10 [/usr/share/dotnet/sdk]

step 3:placing this global.json into solution folder

global.json

old

{
  "sdk": {
    "version": "3.1.301"
  }
}

new

{
  "sdk": {
    "version": "5.0.100-rc.1.20452.10"
  }
}