I tried all the suggestions on the link page(s) but the one I missed and have now found works for me is the batch file method as follows
To clarify how I found the process works…
I made the batch file and named and placed it in my folder of choice
Then when I opened in PL the Export Application and used the Browse to navigate to the previously created folder. Edit ~ to ensure that you can see All Files and not just .exe as the PL system demands…in the Item Selection box put an * (the good old Windows wildcard) and press enter and that will reveal All Files in righthand side window
Clicking on the .bat file adds it into the file name box
Clicking Open completed the process.
Thereafter picking the named choice in the drop-down box in the Export Application dialogue box activates the batch file which triggers a command box in the background and starts Affinity Photo 2
HTH helps others to keep trying
PS the thread where the explanatory posts can be found here
Post here
And here