Is Enlightenment a momentum with a continuum or can have regressions? According to buddhism , does the enlightenment have a continuum from an initial momentum or can have also regressions?
I suppose if a specific state of mind has been acquired from innumerable causes it can’t return back, can just evolve toward a vector even if we force ourself in a condition of ignorance, so the bodhisattvic principle.
Do you see an old woman or a young one? Or can you see both?

Once you've seen, can you forget how to see it?
Until we see the world as it is we don't see it, but once we've seen it we cannot 'unsee'. We may fall back on old habits and patterns (old ways of seeing the world), but enlightenment (honestly) is just seeing the world as it is. It's our natural state, something we're drawn away from by our egoic selves, but which pulls us back to itself whenever we stop fighting against it.
I know, sometimes people feel the need to walk all the way around the block to get back to their own front door; the craving for progress can delude us as easily as any other craving. C'est la vie.