With "Settings → Show archived entries" checked, right-click on a timeframe in the list and choose "Archive". This does not yet change anything visually, but after unchecking and re-checking the "Settings → Show archived entries" the timeframe is shown with the icon indicating "archived".
That icon is probably meant to be shown right away when archiving timeframes.
jansorg
commented
5 years ago
With "Settings → Show archived entries" checked, right-click on a timeframe in the list and choose "Archive". This does not yet change anything visually, but after unchecking and re-checking the "Settings → Show archived entries" the timeframe is shown with the icon indicating "archived".
That icon is probably meant to be shown right away when archiving timeframes.
tom-ui0.7.3 here.