'Elles rentrent après le bus les a déposées' is this wrong because le bus is the subject of the subordinate clause? Bearing in mind this: https://www.lawlessfrench.com/grammar/apres-vs-derriere/ which suggests native speakers do whatever they can to avoid apres que?
Yes, it's wrong because 'le bus les a déposées' is a subordinate clause where bus is the subject followed by a verb. As such it needs to be preceded by 'après que'.
'Après' without the 'que' is only used before words or phrases that don't involve verbs.
That thoughtco article is saying that the preferred French style might be to say something like 'après leur descente du bus'; or something without a verb to avoid the inelegant but correct 'après + que + clause with verb' construction.
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