Hello,
You can double click on the project in solution explorer, for the PropertyGroup use this setup, save, build and the web browser control will be in the toolbox. If not C# remove the LangVersion and nullable elements.
<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
<PropertyGroup>
<OutputType>WinExe</OutputType>
<TargetFrameworks>net48;netcoreapp3.1</TargetFrameworks>
<LangVersion>9.0</LangVersion>
<Nullable>enable</Nullable>
<UseWindowsForms>true</UseWindowsForms>
</PropertyGroup>
</Project>