I think you are calling ākāsānañcāyatana, viññāṇañcāyatana, ākiñcaññāyatana, nevasaññānāsaññāyatana as Upanishads immaterial jhanas
I dislike entangling with hifalutin words...
unless you elaborate, some are defined in MN 111 as Buddhist. For a person at the beginner level of jhana (definitely non-returner nor Arahant), these do not make sense.
If you are familiar with the Upanisad modes of these, what do you experience?
My understanding is these are dwellings of bliss, but the conundrum for me is, in the third
Buddhist jhana which I am familiar with, the meditation is about gaining insight to
impermanence (snake with three rings, simile used) so that rapture is discarded. Rapture/bliss stands
in the way of entering 4th jhana. If so why look for bliss after the 4th jhana,
in modes 5, 6, 7 etc. afterwards. Does it make sense?
My understanding? if I go with the AN 9.36(what i searched up to copy paste the pali words for the list of things what are coming after 4 jhanas) then you need only 1st jhana to gain liberation.
Your wording here is not clear to me, is this a question? Few suttas in the canon do say first jhana is sufficient to achieve the goal. It may be so for the resolute meditator, who is immersed in the 37 factors of awakening.
MN 121 does not refer to jhana as such at all, but offers instructions as to how to get to the void. Many
folks do not know how to interpret this unique sutta, it is not that unique in a way.
Moggallana used to meditate in this fashion.
Knowing that above,then i assume when you do it in 1st jhana then your mind is liberated from rebirth to 1st jhana and where you will be is 2nd jhana. The 'no more rebirth' extends to the corresponding world it is attained, so if you get 4 jhana defilement eradicated you will going to abide in 5th once this body is expired.
Your comment baffles me, please make it clearer.
Let us try to be on the same page as regards the goal of Buddhist Jhana. I perceive it as the crowning of the 4 establishments of mindfulness, or vice versa. These cannot be separated from other practices used for awakening, in the process of wiping out the afflictions.
Once you told me the eightfold path does not concern you.
Leaving aside the other factors, let us consider right view, right thinking (same sankappa), if one does not pay serious attention to these, one might as well forget about right sati, and right samadhi (4 jhanas)
Some folks are impressed by buddhist jhana, for the wrong reasons. Certain places of the canon says
via jhana one can walk through walls, gain divine ears, examine past lives.
Not even Sariputta was interested in these literally. Why should we be? If you are curious about
Buddha's teaching for these reasons, then you are in the wrong class room.
Once you respond to the above I will explain what transcending sensual sphere means.
Have a splendid weekend dear Auto.