The “perfect and unexcelled enlightenment” is that in which there’s a realization that there was never a path, nor enlightenment.

Arahants and Boddhisattvas reside in Nirvana. Buddhas reside in a place where there is no distinction between Nirvana and Samsara. It is beyond that distinction. Which is why Buddha’s Nirvana is also sometimes called “non-abiding”.

Another way to put it is that they attained non-attainment.