This teaching on anātma or non-Self is complex and vexed and there are many views of what it actually means.
The Buddha himself spoke of “self” right up until the moment of his liberation - affirming the existence of an “I” - provisional as it may be.
He also made the following observation of one knowing that one is free - there is no “Self” what is it that knows it’s own freedom?
Buddha also affirms that he had many previous births and that the Bodhisattva (potential Buddha) had to wander through countless lives, four asankhyeyyas and one hundred thousand world-cycles (kalpa = 4,320,000,000 yrs) with the noble, determined performances of the Bodhisattva virtues to win full Enlightenment or Sammásambuddha ñana (Supreme Enlightenment).
The view that it was just a flow of ever-changing consciousness doesn’t explain detailed memory of past births.
Recollection of Past Lives - Digha Nikaya Samaññaphala Sutta: The Fruits of the Contemplative Life
"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the recollection of past lives (lit: previous homes). He recollects his manifold past lives, i.e., one birth, two births, three births, four, five, ten, twenty, thirty, forty, fifty, one hundred, one thousand, one hundred thousand, many aeons of cosmic contraction, many aeons of cosmic expansion, many aeons of cosmic contraction and expansion, [recollecting], 'There I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose here.' Thus he recollects his manifold past lives in their modes and details. Just as if a man were to go from his home village to another village, and then from that village to yet another village, and then from that village back to his home village. The thought would occur to him, 'I went from my home village to that village over there. There I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I went to that village over there, and there I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I came back home.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the recollection of past lives. He recollects his manifold past lives... in their modes and details.
"This, too, great king, is a fruit of the contemplative life, visible here and now, more excellent than the previous ones and more sublime.
The Buddha describes Nirvāna in both positive and negative terms as a state of experience. So naturally the question arises - if there is no “Self” then who or what experiences Nirvāṇa? If Nirvāna is just negative state annihilation then why describe it at all?
The Buddha gives 30 metaphors for nirvāna – nibbana (SN 43.14)
asankhata – unconditioned,
antam – the end,
anasavam – disease free,
saccam – the truth,
param – the ultimate,
nipunam – the subtle,
sududdasam –very hard to perceive,
ajaram – imperishable,
dhuvam – the stable,
apalokitam – the taken leave of,
anidassanam – cannot be demonstrated,
nippapam – without impediment,
santam – the peace,
amatam – the deathless,
panitam – the excellent,
sivam – the auspicious
khemam – the secure,
tanhakkhaya – the destruction of craving,
acchariyam – the wonderful,
adbhutam – the astonishing,
anitikam – freedom from harm,
anitikadhammam – the state of freedom from harm,
nibbanam – extinction,
avyapājjho – the harmless,
virāgo – non-attachment,
suddhim – purity,
mutti – liberation
analayo – the done away with,
dīpam – the island,
lena – the cave,
tanam – the shelter,
saranam – the refuge,
parāyanam – the ultimate goal.
anasavam – disease free,
saccam – the truth,
param – the ultimate,