From the viewpoint of modern Western psychology, the 'subconscious' is explained as follows:
The subconscious is the part of our mind that is not in current awareness. It is the part of our consciousness that is not being
focused on and is lying dormant. It is impossible to hold the entirety
of our knowledge in direct focus in our minds at the same time so we
need to store memories and knowledge. This storage is known as the
subconscious, the term being coined by Pierre Janet. The subconscious
stores all of your memories, beliefs, previous experiences, the
people/places you have seen, and the skills you have acquired.
Information in the subconscious cannot be recalled easily, they are
buried deep within our minds (or repressed).
https://www.alleydog.com/glossary/definition.php?term=Subconscious
The closest Pali term to 'subconscious' is 'anusaya' or 'underlying tendencies', as follows:
Mendicants, there are these seven underlying tendencies. What seven? The underlying tendencies of sensual desire, repulsion, views, doubt, conceit, desire for becoming and ignorance. These are the seven underlying tendencies.
AN 7.11
'Anusaya' can flow out or erupt from the subconscious into consciousness. This 'outflow' or 'eruption' in Pali is called 'asava'. The product or result of these anusaya flowing out are called 'hindrances' ('nivarana').
Therefore, on a gross level, it appears it is the hindrances themselves which are the 'subconscious' coming into consciousness.
When the hindrances end, what occurs is the bliss & equanimity of jhana; which is obviously not 'the subconscious' referred to by modern Western psychology.
However, on a very subtle level, when a jhana attainer recollects their 'previous dwellings', 'past ego adherences' or 'pubbenivāsa' (described in SN 22.79), this appears to be an example of genuine insight (vipassana) in relation to the 'subconscious'.