Depending on the scale, the timeline shows days, months, quarters, or years. You can adjust the scale to your needs to display long-lasting projects in their entirety.
You can zoom all the way down to daily granularity to see non-working days. They will be hidden once you zoom out to see quarters of the year on the timeline:
Scale to fit
If you have a lot of important information on you task list you may want to adjust the timeline to fit all tasks in the available area of your screen. Use the "Scale to fit" option to adjust the timeline so it shows all your tasks sorted from the earliest start date to the latest end date.
Additionally, since the Bird View feature is no longer present in the app, you can use "Fit to scale" functionality to display tasks that aren't visible in their entirety when you have reached the limit of "zoom out" option.
Maximum level of zooming out has been reached. The task only partially fits on the Gantt timeline.
After clicking the "Scale to fit" button the entire task fits the timeline.