It may seem a basic question, but I have come to what seems to be a very different understanding to the general one. I think we would all agree on the Pali text e.g. at https://suttacentral.net/pi/dn22#82:
Katamañca, bhikkhave, dukkhaṃ ariyasaccaṃ? Jātipi dukkhā, jarāpi dukkhā, maraṇampi dukkhaṃ, sokaparidevadukkhadomanassupāyāsāpi dukkhā, appiyehi sampayogopi dukkho, piyehi vippayogopi dukkho, yampicchaṃ na labhati tampi dukkhaṃ, saṃkhittena pañcupādānakkhandhā dukkhā.
Translations are where we might disagree on:
“Now what, monks, is the Noble Truth of Suffering? Birth is suffering, old age is suffering, death is suffering, grief and lamentation are suffering, sorrow and despair are suffering, being joined to what is not liked is suffering, being parted from what is liked is suffering, also not to obtain that which one longs for is suffering. In brief, the five clung to aggregates are suffering.”
In this translation I read ‘sokaparidevadukkha’ as ‘grief and lamentation are suffering’. I don’t read ‘dukkha’ there as ‘pain’ and to get: ‘grief, lamentation, pain’, but read dukkha there with the same meaning it occurs in the other eight occurrences in the paragraph. Thus, to me, only the first three items (birth, aging and death) could be interpreted as physical and all the others are mental.
To me, the summary sentence ‘In brief, the five clung to aggregates are suffering’ would be accurately paraphrased as: five aggregates (life) / + clinging / = suffering. And the summary of the First Noble Truth as ‘Life is Suffering’, is certainly not accurate, as it leaves out ‘clinging’, but understood to have come from the belief that birth, old age and death are meant there to be physical.
I note that the summary sentence is not:
saṃkhittena pañcakkhandhā dukkha
in brief the Five Aggregates are suffering
which to me would mean ‘Life is suffering’.
Unfortunately, I have not found ‘Life is Suffering’ which in Pali would be ‘jīvitam dukkham’ anywhere in the Tipiṭaka by a digital search. So to me, the belief that the First Noble Truth means that, is just an interpretation, even though a very popular one.
Now dealing with the first three terms usually taken as physical and seemingly having texts to explain them as such, I have found repeated times the Buddha is recorded to have given psychological meanings (redefinitions) to key terms, clearly including ‘death’.
“For this, monks, is death in the Noble One’s Discipline: that one gives up the training and returns to the lower life”
So, for me Nibbāna is the fading away and cessation of the Five Clung to Aggregates, not the Five Aggregates and the Buddha realised complete Nibbāna (parinibbāna) under the Bodhi Tree and lived a happy life (without birth aging and death) for 45 years till the ‘breaking up of his body’ (kāyassa bedha) which is the phrase he most often used for the end of life of a arahant, not ‘death’. And terms with parinibb* were used mostly to refer to the living arahant.