If you say that something is insupportable, you mean that it cannot be coped with or accepted.
Too much spending on rearmament would place an insupportable burden on the nation's productive capacity..., Life without Anna had no savour, was tedious, insupportable.
Translation English Cobuild Collins Dictionary
1 insufferable, intolerable, past bearing, unbearable, unendurable
2 indefensible, unjustifiable, untenable
English Collins Dictionary - English synonyms & Thesaurus
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