This is somewhat minor, but I do feel that picking dates is a little more cumbersome than it should be (in the pop-up date pickers for Entity views). There are, I think, two reasons for this.
First and perhaps most broadly, dates in the past are not grayed out or otherwise indicated as being passed as they often are in other systems. This can be a quick and helpful way to orient yourself on the calendar mini-view. And typically I am not needing to select dates in the past, as I would guess is true for many people.
Second, it seems the the positioning of days on the calendar is “wrong” in Fibery. They are offset 1 day from my normal calendars. I’m not sure if this is a difference of what day is considered the “start” of the week, or something else. But here’s an image showing the Fibery date picker next to the Windows calendar, and you can see that today, Tuesday the 15th, is in the second column in Fibery, but in the 3rd column in Windows.
The Windows version is how all my other calendars show it as well, so I’m definitely used to that. For example ToDoist also has it this way as well.
Adding a “date is in the past” visual indicator would help a lot, as would at least an option to change the layout of dates to match what I’m guessing are US style calendars.