OK i managed to solve this issue. I first needed to install the certificates to the local machine either from the certificates folder which is inside the layout folder or by right clicking the setup.exe and then Properties - Digital signatures - click on the item in the list then click Details - view certificate - install certificate - Local machine and then just continue the process with the defaults.

Then once the certificates are installed i then run the .exe as administrator and it works :)

Microsoft no longer offers offline installers such as .ISO images of Visual Studio -- instead they have instructions of placing the burden on you to create an offline installer. You need to use the --layout command line argument and then run the downloaded installer.

1. Download and Cache offline files:

   vs_community.exe --layout f:\vslayout.2019 --lang en-US
   

2. Run from the cached directory

   f:
   cd \vslayout.2019
   vs_community.exe --noWeb
   

NOTE: Change drive F to match a drive on your system that has ~35 GB of free space for MSVC 2019. See the instructions for command line arguments to select just C++, .NET, etc. options.

You can get help on the command line arguments for the installer via:

vs_community --help

The relevant layout commands are:

command-line option     Description
--layout <dir>          Specifies a directory to create an offline install cache.
--lang <locales>        Used with --layout to prepare an offline install cache with resource packages with the specified language(s). See a full list of supported language-locales below.
--add <workload>        One or more workload or component IDs to add. The required components of the artifact are installed, but not the recommended or optional components. You can control additional components globally using --includeRecommended and/or --includeOptional. For finer-grained control, you can append ;includeRecommended or ;includeOptional to the ID (for example, --add Workload1;includeRecommended or --add Workload2;includeOptional).
                        Note: If --add is used, only the specified workloads and components and their dependencies are downloaded. If --add is not specified, all workloads and components are downloaded to the layout.
--includeRecommended    Includes the recommended components for any workloads that are installed, but not the optional components. The workloads are specified either with --allWorkloads or --add.
--includeOptional       Includes the recommended and optional components for any workloads being included in the layout. The workloads are specified with --add.
--keepLayoutVersion     Apply changes to the layout without updating the version of the layout.
--verify                Verify the contents of a layout. Any corrupt or missing files are listed.
--fix                   Verify the contents of a layout. If any files are found to be corrupt or missing, they are redownloaded. Internet access is required to fix a layout.
--clean <paths to catalogs>