At the moment, the default settings for screenshots is "keep for 3 days". Sometimes, an installation/update can revert the settings to the default, which will automatically delete all screenshots older than 3 days. For me, it deleted over a year's worth of screenshot data as a result of an update. Fortunatelly, not all was lost as I had a backup of some of the data.

The system should include a test that if it needs to delete an unexpectedly large number of screenshots, it warns you in advance. The prompt could be something like "Manictime will delete X as a result of a change in settings. Would you like to proceed" (where X could be the number of folders (i.e days) to be deleted, or the number of screenshots, or just the text "a large number of screenshots") with the buttons being "Proceed" (in which case the files are deleted) and "Change Settings" (in which case, the files remain, and you are taken to the settings menu to adjust the screenshot settings).

In normal practice, when the system is just deleting the expected number of screenshots as a result of the reaching the days/size limit under the current settings, this pop-up message would never appear.

Backstory:

I'm using the free version of MT on Windows for self-tracking for over 3 years.

Recently I wanted to see total time working on particular drawing, and I was able to do it like this:

Statistics - Custom - Add - Timeline: Documents (at top) - Files (at left).

Now at right there is a huge list of filenames gathered in these years, some with paths, some not, even some with quirky path formats like "(D:) drivename / path / deeperpath / file_name.ext" (with parentheses, slashes and spaces exactly like that).

The filelist takes around 10 seconds each time to generate or sort.

At first, every file was checked. I selected all with Ctrl+A (works instantly), clicked one of the checkboxes (MT client UI went unresponsive for several minutes, maybe over 10 min), then everything became unchecked.

I found some files I wanted to sum and checked them back (one by one it works instantly too).

Finally, refreshing all statistics takes around 5 seconds, less than generating the list of files in UI.

Suggestion:

It would be a lot easier to enter some pre-known filename wildcards, than digging in the filelist. Simplest I can think of - one pattern per line in a text area, that could be shown instead of checklist by an option. For example, using radio-buttons at bottom of "Edit Statistics" dialog:

Match:
- checklist any
- checklist all (only show/enable for the Tags timeline?)
- wildcard any
- wildcard all.

The proposed feature could be like:
Select a time frame, Right Click, choose "Preserve screenshots".
And the screenshots within this time frame will not be automatically deleted.

The reason I want this feature is because screenshots may provider more help other than logging times. Take the motive of this PR as an example. I had a research on one problem in our system recently and had some progress. However, the clues are still not enough to solve the problem, and the chance this problem occurs would be very rare so other works take advance of it, which may last several weeks before I can work on this problem.
If at the time I return to this problem, all the screenshots when I research on this problem are still available, they could provide great help for solving it.