If I understand the explanation above correctly, "to be not a big deal" works well.
However, I think it really depends on the context.
Other options I can think of include:
(There is) no need to criticize(There is) no need to play the blame game(There is) no cause for judgementto be not his/her/their fault/ to be nobody"s faultto be reasonable/understandable
More context would be helpful for answering this question.
無可厚非，成語。漢語拼音為wú kě hòu fēi ，表示沒有可過分責難的。
If I understand the explanation above correctly, "to be not a big deal" works well.
However, I think it really depends on the context.
Other options I can think of include:
(There is) no need to criticize(There is) no need to play the blame game(There is) no cause for judgementto be not his/her/their fault/ to be nobody"s faultto be reasonable/understandableMore context would be helpful for answering this question.
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栗子的知乎答案索引：栗子樹
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