I am reproducing the question content hereunder:
In Nasadiya it is mentioned that even creator might don't know about
creation. on the other side Rigveda (10.121) mentions the
Hiranyagarbha ("golden embryo") as the source of the creation of the
Universe.
I had already expressed my opinion on The Nāsadīya Sūkta. RV X.121.1 says,
The golden embryo evolved in the beginning. Born the lord of what came
to be, he alone existed. He supports the earth and the heaven here— –
Who is the god to whom we should do homage with our oblation?
Brereton and Jamison in their translation to RV X.121, say as follows:
This hymn takes the form of a cosmogony, but here the creative
principle is unnamed or has no name. Rather than declaring its deity,
the hymn’s refrain is a question: “Who is the god to whom we should do
homage with our oblation?”
This questioning about creator - “Who is the god to whom we should do
homage with our oblation?” continues even in the subsequent 8 mantras.
However, it was only in 10th Mantra of RV X.121 that the creator was named as prajApati.
prajāpate na tvadetānyanyo viśvā jātāni pari tābabhūva | yatkāmāste
juhumastan no astu vayaṃ syāma patayorayīṇām ||
O Prajāpati! No one other than you has encompassed all these things
that have been born. Let what we desire as we make oblation to you be
ours. We would be lords of riches
As pointed out by Brereton and Jamison, the last mantra might be a later day addition, as it deviated from the preceding 9 mantras, which said “Who is the god to whom we should do
homage with our oblation?”.
In 8th mantra it was said the god over gods, alone existed (deveṣvadhi deva eka āsīt).
It is similar way of saying गणानां त्वा गणपतिं - Lord and Leader of the heavenly hosts - in RV II.23.1
gaṇānāṃ tvā gaṇapatiṃ havāmahe kaviṃ kavīnāmupamaśravastamam |
jyeṣṭharājaṃ brahmaṇāṃ brahmaṇas pata ā naḥ ṣṛṇvannūtibhiḥ sīda
sādanam ||
In my opinion, both X.121 and X.129 are saying the same idea - the creator is unknown .
Further, hiranyagirbha (golden embryo) is an epithet referring to source of creation.
In X.96.5 it was stated that SOMA, again an epithet for BLISS, is the creator of all Gods, including Indra, Vishnu, etc.
Soma purifies himself—the begetter of poetic thoughts, begetter of
heaven, begetter of earth, begetter of Agni, begetter of the sun,
begetter of Indra, and begetter of Viṣṇu
Hence, we should not get confused with the epithets to be as real things.