A new idea for a feature

Is there an option to rewatch a serie or movie for a second time and still keep track where you are?

There is not. It is something we have been recently investigating how to implement

There is already a feature request here you can vote on. Mark for rewatch

For now, mark the whole series as unwatched, then start watching episode 1.
Episode tracking will work as expected.

That’s what I do. No big deal