how to install dotnet core on ubuntu 20.4?

Question

I'm trying to install Dotnet core on my server with this commands.

wget https://packages.microsoft.com/config/ubuntu/20.04/packages-microsoft-prod.deb -O packages-microsoft-prod.deb
sudo dpkg -i packages-microsoft-prod.deb


sudo apt-get update
sudo apt-get install apt-transport-https
sudo apt-get update
sudo apt-get install dotnet-sdk-3.1

but the output of "dotnet --version" is

It was not possible to find any installed .NET Core SDKs

and when i went to root directory of my project and and use "sudo dotnet build -c Release" the output is

      It was not possible to find any installed .NET Core SDKs
  Did you mean to run .NET Core SDK commands? Install a .NET Core SDK from:https://aka.ms/dotnet-download

Does anyone have an idea?

=========update=========

I used Docker and all my problems were solved