When we open the timeline settings, we have the issue display range where we can select for how long (in months) completed issues will keep appearing in the timeline view.

The filter is based on the due date field, which is not ideal for some customers. 
If the issue is associated with a sprint, it will use the sprint due date value.
If the issue is not associated with a sprint, it will use the issue's due date value.

That's my suggestion for improvement:

Some customers won't associate the issues with a sprint; neither will they use the due date field. Those customers won't have the option to hide completed issues.

As a Jira Software user, I would like the implementation of a new filter to allow users to display issues based on their resolved date instead of their due date, allowing them to hide completed issues without using the due date field.