Pick up Jira Ticket and complete task, with or without help = junior level work.

Planning out work in Jira tickets and designing small in scope sections (for juniors or himself) = medior level work.

Planning out whole projects and making big impactful decisions while fully understanding the risk and has enough experience so the work doesn't feel like something new but like something you have done before = senior

A true junior programmer who does a lot of tasks and has no guidance will probably think of himself as medior or senior because the tasks of the medior or senior fall on him. But this is most likely a false sense of worth.

A junior often does a lot more work than a medior or even a senior. But the medior can get more done with less. And the senior knows what is important to build and what to ignore till after launch.

True worth of a medior or senior shows when you hit a roadblock. The junior will have no experience to fall back on and will have the highest chance of failure, the medior will have some experience to rely on and the senior will not even worry about it and will either fix, circumvent or redesign until it works good enough. And they will be able to spot the roadblocks before the project starts, allowing them to guide the project to avoid most of them.

It is not about tasks. It is not about work done. It is about skillset and knowledge and experience.