I dislike defining seniority by your technical knowledge or skills. I have a different, I think more useful definition that I use. It overlaps a little bit but excludes knowledge, intelligence and focuses on mindset and ownership.
More senior person is one that has more mature approach to their work. One that can get better results with less resources. Typically more senior people can also accept wider variety of tasks.
What is better results and what is less resources will depend on the project.
It has nothing to do with the knowledge or experience, in my opinion.
You can have good senior person get better results in a technology they have no previous experience with compared to a very experienced / intelligent / knowledgeable person that has track record of making bad decisions. Senior person will use their good judgement to warn the manager they are running outside of their knowledge and to know when they need to use some resources (like help) from somebody more knowledgeable.
A knowledgeable but less senior person may think they know anything but not be able to recognize they are trying to achieve something that is outside their area of expertise or not be able to recognize or accept they are bad at something.
For me senior developer is somebody I can entrust they will put honest, worthwhile attempt at making good decisions when it is called for and recognize when they need to come back for further direction.
Senior developers show ownership in that they seek to uncover problems and discuss those problems with the team, proactively and productively. Senior developers can smell problems even if they don't necessarily know the solution. They can act on the signs of the bad smell and maybe seek discussion (with architect? client? manager? team?) to figure out what is going on and what needs to be done further.
Senior developers understand there are many ways/levels to solve the problem and sometimes solution isn't more code but maybe procedural change or a shift in paradigm.
Senior developers can meaningfully help/direct more junior team members individually without taking over their projects.
Senior developers can keep working relationships even with difficult people or people they don't like.
And so on.