Hi Jafo, thank you for your kind suggestion. Although I have been using computers for well over 40 years - so I am a very experienced user, nevertheless when it comes to technical things it is still possible for me to come unstuck at a relatively basic level, so I might display an amusing level of ignorance which you may need to rescue me from !
Ok, so the latest three programs which I am attempting to add to OD's Tabbed Dock are all apps in Serif's Affinity range, Serif being a UK company. As a very long time user of their products I also own their now obsolete Plus range products. I'm telling you that because all four Plus apps are happily sitting on the Tabbed Dock and work correctly from it.
To test your suggestion, I re-created a shortcut icon onto the computer desktop of one those old apps, PagePlusX9. I then right-clicked to get Properties of it. On the Compatibility tab, the top text reads as follows: "If this program isn't working correctly on this version of Windows, trying running the compatibility troubleshooter." I don't need to do that as it, and it's other three sister apps all work correctly. I'm running Windows 64-bit OS x64-based processor, Edition Windows 10 Pro, Version 20H2, with the Windows Feature Experience Pack.
All three of the new Serif apps also work correctly on my machine - they were built from scratch and released as an entirely new range for both Mac and Win10 machines quite late in 2014 - with their predecessors, the Plus range, being discontinued, as I've indicated.
With reference to your mention of compatibility modes, as a double check, I've opened Properties on Affinity Photo as well as PPX9. As you can see in the screenshot below, both are set the same in the Compatibility mode section - ie. NOT ticked, so neither Win8, (or any of the earlier versions in the drop-down menus, - Vista, Win7, etc) have been applied to either app.
