＞ 謝る is intransitive and never takes a true direct object.
＞ In this sentence, the を is not marking a direct object; instead, it indicates what the apology is about and can be understood roughly as "about" or "for" in English.
Do you have references for this? I was unable to retrieve this sense from dictionaries. It seems very english-derived.
To my knowledge only "移動や時間の経過を表す自動詞" (Meikyo) and intransitive verbs in a starting point construction (e.g. 家を出る) can take を (and still be intransitive).
Also, the english translation being an intransitive construction is not a criterion.
While DOJG also has also a fourth usage for を, "A particle that marks the cause of some human emotion.", 謝る doesn't really fall into that category in my eyes.
The examples DOJG gives contain verbs of emotion that are frequently tagged as transitive or bitransitive by references (e.g. 喜ぶ, 恐れる, etc.).
＊ Data
Massif:
｛を謝る｝＝ 524
｛に謝る｝＝ 3899 (false hits possible)
BCCWJ:
｛を；謝る｝＝ 11
｛に〈格助詞〉；謝る｝＝ 36
References that have 自動詞 ＝ Nikkoku
References that have 他動詞 ＝ Sankoku, SankokuGendaiGairai, Oukoku, Smk, Meikyo, Shinsen
References that have 自他動詞 ＝ Kojien, Gakken Kokugodaijiten, Iwakoku
Smk: 〈だれニ（なにヲ）謝る〉
To me the following examples, taken from various references, look perfectly transitive:
「うそを言ったことを謝る」
「人に罪を謝る」
「弟の不始末を姉が謝る」
「彼女は先生に遅刻したことを謝った」(e.g. replacing を with に here seems weird/ungrammatical to me)
Interestingly my 古語 references have 謝る is intransitive.
It seems 謝る came from 誤る, which was originally the intransitive pair to 過つ, which appears to have fallen out of use.
(Wiktionary, Nikkoku, Koj)
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Another problem is that the english concepts of transitive/intransitive may not perfectly map onto 他動詞 and 自動詞, as pointed out be the following usage note on wiktionary: https://en.wiktionary.org/wiki/他動詞
"The terms transitive and intransitive are somewhat misleading in reference to Japanese. The English terms are generally used to refer to the syntax or structure of a sentence, and whether the verb in the sentence is followed by an object. The Japanese terms refer to the semantics or meaning of the verb, and whether the action of that verb is happening to or upon something else. The Japanese term 自動詞 (jidōshi) literally means “self-acting word”, and 他動詞 (tadōshi) literally means “other-acting word”, in reference to this semantic consideration.
For instance, in English, the verb ate in the simple sentence “I ate” would be considered an intransitive verb, because it is not followed by an object.
However, in the corresponding Japanese, the verb 食べた (tabeta, “ate”) in the simple sentence 私は食べた。 (“Watashi wa tabeta.”) would not be considered a 自動詞 (jidōshi), but would instead be considered a 他動詞 (tadōshi, literally “other-acting word”), as the underlying semantics or meaning of the verb 食べる (taberu, “to eat”) conceptually require an object: when one eats, one eats something, even if left unstated.
This semantic focus is the underlying mechanism by which verbs in sentences like 私は食べた。 (Watashi wa tabeta. - “I ate.”) are still considered 他動詞 (tadōshi, glossed as “transitive”) even when there is no stated object (because the fundamental meaning of the verb implies action by the subject upon something else), and verbs in sentences like 道を歩く。 (Michi o aruku. - “[I] walk the street.”) are still considered 自動詞 (jidōshi, glossed as “intransitive”) even when there is an explicit object marked with the object or accusative particle を (o) (because the fundamental meaning of the verb only implies action by the subject itself in a way that does not affect the noun marked by を)."
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＞ for example, tagging 焦る as transitive [...]
Here I see multiple references having a 自他動詞 tag, with meikyo splitting out a transitive sense.
But that's an issue for another time.
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