I currently use Thunderbird to organize my tasks. I have them pinned to a calendar by their due-date and in a side panel too. However, a major limitation of Thunderbird as a whole is the fact that I cannot attach a start date to a task without it appearing several times on my calendar for each day that it can be worked on. This is pretty annoying and I only want it to appear on the calendar for the date it’s due. I also want my task pane to sort of show the number of days it’s due, whether it can be started yet, and if not, how many days until it can be.
Afaik not many task organizers can do something this complex. I’ve used KOrganizer and its forks in the past but there was too much friction in using it that I switched to Thunderbird.

Have you tried submitting a PR to Thunderbird?
I just mark the due date as an event with a date using Thunderbird’s calendar
I just use Remind, which is the best calendar app ever. If you aren’t happy with the calendar on Thunderbird, do you maybe want to take the step to using a full project management app, like
ProjectLibre, GanttProject, Gnome Planner, et. al?ProjectLibre sounded interesting, but they’re pushing their subscription SaaS product hard. That kind of mindset doesn’t bode well for it’s future. I would look elsewhere. The term “libre” doesn’t belong on paid subscriptions.
What makes Remind awesome?
It’s terminal (well, has a gui if you want) based, which always is a big plus for me. It allows for a lot of tinkering. Here’s a link to the website FAQ, is you want more. Username/Password == notabot/notabot
If you like tinkering, customizing your .*rc files, then you’ll probably enjoy it. If you don’t like the terminal or tinkering with txt files, then your mileage may vary. Although the Tcl/Tk gui is pretty user friendly.
At one point while looking for a calendar app I needed one that could import events from a text file (not ics) and khal was recommended. I was able to import 250 events in one command. I didn’t want a cli calendar, but I ended up just keeping that one installed along with todoman for task lists. It isn’t ideal, but I haven’t noticed the problem you have said about due dates and start dates.
I use Evolution for synced calendar dates and am trying Taskwarrior for flexible tasks (which has many features, but one can keep it simple). Basically, I am using text files (Zim Wiki, Org Mode) for work projects since I like to divide tasks into daily small steps.
Proton calendar because i get the notifications on my phone




