This is a very good question.
Ven. Thanissaro translated SN 36.21 as saying very clearly below that not everything that happens to us is caused by that which was done before. The sutta gives examples like bile, weather, harsh treatment etc. As you have said correctly, MN 101 reinforces the message of SN 36.21.
So any brahmans & contemplatives who are of the doctrine & view that
whatever an individual feels — pleasure, pain, neither
pleasure-nor-pain — is entirely caused by what was done before — slip
past what they themselves know, slip past what is agreed on by the
world. Therefore I say that those brahmans & contemplatives are
wrong."
And yet, in his commentary to the translation of SN 36.21, he wrote that this is not the correct interpretation of this sutta, citing SN 35.145 as stating that the body and mind is old kamma.
SN 35.145 states that the eyes, ears, nose, tongue, body and mind are old kamma, capable of being felt. But, it doesn't say WHOSE old kamma it is.
The suttas below (SN 12.17 and SN 22.85) answer that question.
So, the eyes, ears, nose, tongue, body and mind definitely arise due to old kamma. After all, they cannot arise spontaneously - they definitely arise due to old kamma. But we cannot ask WHOSE old kamma it is. It is dependently originated - with ignorance as the condition.
This is in line with sabbe dhamma anatta (all phenomena is not self).
Based on the following sutta quotes, if we say that OUR body and mind arises due to OUR own past kamma, that's an indication of self-view and it's also the view of eternalism.
If we say that the old or new kamma is not done by anyone, that's annihilationism. But this is also a type of self-view.
Instead, the Buddha taught dependent origination. That the self is impermanent, changing and dependently originated.
So, there is volition and there is suffering, but we don't connect them to a specific permanent self identity.
In AN 5.57, it is stated that one should have the view of "I am the owner of my kamma, the heir of my kamma; I have kamma as my origin, kamma as my relative, kamma as my resort; I will be the heir of whatever kamma, good or bad, that I do". But this is only skillful means (upaya) to cultivate hiri and otappa (shame and fear of wrongdoing).
From SN 12.17:
“How is it, Master Gotama: is suffering created by oneself?”
“Not so, Kassapa,” the Blessed One said.
“Then, Master Gotama, is suffering created by another?”
“Not so, Kassapa,” the Blessed One said.
“How is it then, Master Gotama: is suffering created both by oneself
and by another?”
“Not so, Kassapa,” the Blessed One said.
“Then, Master Gotama, has suffering arisen fortuitously, being created
neither by oneself nor by another?”
“Not so, Kassapa,” the Blessed One said.
“How is it then, Master Gotama: is there no suffering?”
“It is not that there is no suffering, Kassapa; there is suffering.”
“Then is it that Master Gotama does not know and see suffering?”
“It is not that I do not know and see suffering, Kassapa. I know
suffering, I see suffering.”
“Whether you are asked: ‘How is it, Master Gotama: is suffering
created by oneself?’ or ‘Is it created by another?’ or ‘Is it created
by both?’ or ‘Is it created by neither?’ in each case you say: ‘Not
so, Kassapa.’ When you are asked: ‘How is it then, Master Gotama: is
there no suffering?’ you say: ‘It is not that there is no suffering,
Kassapa; there is suffering.’ When asked: ‘Then is it that Master
Gotama does not know and see suffering?’ you say: ‘It is not that I do
not know and see suffering, Kassapa. I know suffering, I see
suffering.’ Venerable sir, let the Blessed One explain suffering to
me. Let the Blessed One teach me about suffering.”
“Kassapa, if one
thinks, ‘The one who acts is the same as the one who experiences the
result,’ then one asserts with reference to one existing from the
beginning: ‘Suffering is created by oneself.’ When one asserts thus,
this amounts to eternalism.
But, Kassapa, if one thinks, ‘The one who
acts is one, the one who experiences the result is another,’ then one
asserts with reference to one stricken by feeling: ‘Suffering is
created by another.’ When one asserts thus, this amounts to
annihilationism.
Without veering towards either of these extremes, the
Tathagata teaches the Dhamma by the middle: ‘With ignorance as
condition, volitional formations come to be; with volitional
formations as condition, consciousness…. Such is the origin of this
whole mass of suffering. But with the remainderless fading away and
cessation of ignorance comes cessation of volitional formations; with
the cessation of volitional formations, cessation of consciousness….
Such is the cessation of this whole mass of suffering.’”
Also from SN 22.85:
"And so, my friend Yamaka — when you can't pin down the Tathagata as a
truth or reality even in the present life — is it proper for you to
declare, 'As I understand the Teaching explained by the Blessed One, a
monk with no more effluents, on the break-up of the body, is
annihilated, perishes, & does not exist after death'?"
"Previously, my friend Sariputta, I did foolishly hold that evil
supposition. But now, having heard your explanation of the Dhamma, I
have abandoned that evil supposition, and have broken through to the
Dhamma."
"Then, friend Yamaka, how would you answer if you are thus asked: A
monk, a worthy one, with no more mental effluents: what is he on the
break-up of the body, after death?"
"Thus asked, I would answer, 'Form is inconstant... Feeling...
Perception... Fabrications... Consciousness is inconstant. That which
is inconstant is stressful (suffering). That which is stressful has
ceased and gone to its end."
Also SN 12.20:
“When, bhikkhus, a noble disciple has clearly seen with correct wisdom
as it really is this dependent origination and these dependently
arisen phenomena, it is impossible that he will run back into the
past, thinking: ‘Did I exist in the past? Did I not exist in the past?
What was I in the past? How was I in the past? Having been what, what
did I become in the past?’ Or that he will run forward into the
future, thinking: ‘Will I exist in the future? Will I not exist in the
future? What will I be in the future? How will I be in the future?
Having been what, what will I become in the future?’ Or that he will
now be inwardly confused about the present thus: ‘Do I exist? Do I not
exist? What am I? How am I? This being—where has it come from, and
where will it go?’
