I'm not entirely sure this correct. I was taught explicitly that les pronoms relatifs composés are NOT used with verbs. If the «de» is attached to a verb one should always use «dont».
Here is a summary when to use dont and when duquel/de laquelle/desquels/desquelles:
My grammar book agrees with the Kwiziq lesson here, but says that dont is more common. Using duquel with a verb is perhaps largely restricted to literature. According to CNRTL, it can substitute for dont:
2. [En emploi littér., par souci de clarté; en fonction de compl. de subst., d'adj., de verbe ou de loc. verbale]
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