Hi Neville,
Indeed the 2019 Run-Time Engines are not yet available in BLT. The main reason is that NI changed the way they release their installers in 2019. Now everything is done using NI Package Manager and NI doesn't publish any more EXE installers for their run-times.
We are working on improving this experience in BLT to support NI Run-Time Engines 2019 and later. In the meantime, here is the approach that we have used internally and with other customers.
1. Install WinRar on your computer
2. Download the LabVIEW Run-Time Engine 2019 SP1 Offline Installer from https://www.ni.com/en-ca/support/downloads/software-products/download.labview.html#329458
3. Extract the downloaded iso file using WinRar:
4. Select all the extracted files and folders and add them to a new WinRar archive:
5. Check the box "Create SFX archive" to create a self-extracting archive
6. Go to the Advanced tab and click on "SFX options..."
7. Configure the SFX options as shown below:
8. Click OK and OK again to create the archive. This will create an EXE file that will extract the NI Run-Time Engine and launch the Install.exe program
9. Configure your BLT Installer to include and launch the SFX archive file you've just created:
Hope this helps.