should I consider 2 different major versions of an application as 2 different projects or just one project
Assume my team is developing an App like Skype. We just delivered 5.0.0 and are planning to develop version 6.
Should I create a new "Project" in Jira, to manage the development of version 6?
One of my concerns is, if I put from skype 5.0.1 to skype 6.26.1, all versions in one project, it seems like the project will never be finished until the product is closed forever.
It absolutely depends on what that "major version" actually is, when compared to the previous one.
Sometimes, a "major version" adds new features to the system but does not make major changes to the existing software (and hardware?) infrastructure, while at other times the exact opposite is true.
Therefore, I would turn to your team as the Subject-Matter Experts (SMEs) here: how do they regard the nature of the new version with respect to the existing one? Are they planning to do rewrites? How much of the existing code-base must they now "touch?"
Perhaps you could briefly present the two alternatives to them, explain the different ways that each might be regarded by themselves and by management, and ask them which option they think would better reflect the task at hand? Because, they're the ones who know best, and it would make a big difference in your reporting ... and, the validity of those reports ... if you "guessed wrong" and were, well, "guessing." Ask the SMEs: the team itself.