No need to apologize, but at https://www.duplicati.com/, the page-top link to “Manual” is easier than threads. Maybe https://forum.duplicati.com/ could also link to that someday? There’s actually your exact wish shown:
This appears under “The retention can be set in 3 ways” in Creating a new backup job, but because yours exists, see Editing an existing backup. One recent addition which you just installed with 22.214.171.124 beta is that there are now 5 ways which have summary help in the UI if you pick them. For (possibly way too much) detail, see the announcement at New retention policy deletes old backups in a smart way and decide if you prefer a simple age-based cleanup or something that thins out old backup versions more as they get older. Perhaps all is fine now from a space point of view and you can file this away for when space does get tight.
Getting back to versions though, I’m concerned that you think you have 100 My Pictures when your screen shot shows 2, with the last one at 03/09/2018 even though you have a scheduled job checking for updates. This might simply mean you don’t actually update anything, thus no new version is made, but please check. Somewhat odd is that a pure pictures backup shouldn’t be smaller than the source (no compression done), but maybe you have some other things there that are not subject to the –compression-extension-file policy.
This isn’t a backup, but the part of the backup that’s a list of source files in that one. You also get dindex and dblock files as seen on your screenshot. These store the file contents and indexes about how to get to them.
Restoring files from a backup should show how many versions you have (should agree with the main screen) and also when they were made. Looking at the file view and maybe even trying a test restore would be good.
Especially if your Duplicati is a Windows Service (would have needed command line work at initial install time) you might have seen Activate downloaded upgrade sometimes fail which is currently getting some discussion.
That’s my attempt to further clarify what everyone is talking about (thanks!), and to suggest another concern.