Our "Timeline" view in Jira (Software project) is not usable. Our list of epics show (child tasks also when expanded) but there is nothing to interact with or visible for the actual timeline. There are no boxes that show any duration of time, that you can see or interact with.

I've been reading around the topic and it seems a little fragmented. For example in this video you can see on the left sidebar there is a "Roadmap" view:
https://www.youtube.com/watch?v=8nbJgvMf0hc
We do not have that... It just says "Timeline" instead.

There is no data in our "Task" or "Epic" type to add a start or end date. I took a look at the fields in the admin and it's locked with no option to enable it or indication of what the consequences of doing so would be.

Is the reason that this feature is not possible to use?