Okay I've found why the PostJam version is not the default to install. The Jam version's data file lists the Jam version as having been updated 26th November, 2023 but the PostJam version is listed as having been created and updated at 23 May 2023 so the app finds the latest version to be the Jam submission and therefore installs that by default and it is not obvious from the interface that there are other versions... indeed the "Install" button is visible once seeing the very top of the page so someone my never see the list of versions before deciding to install the programme and then the drop down for other versions exists whether there are other versions in that dropdown or not and so it is not clear if a programme has an alternate version without active clicking on the dropdown to find what other versions there are.
All this means that since your latest updated version (according to the metadata the app uses) is the Jam version that was "updated" 26th November 2023 and so that is given as the default (by the looks of it). I presume that, if nothing else, you "update" the PostJam version this issue will be fixed nd you'll stop getting so many reports about the Jam version! ;) <3