The Incapacitated condition says:
An incapacitated creature can’t take actions or reactions.
Can someone who is incapacitated still take bonus actions?
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From the rules for bonus actions:
anything that deprives you of your ability to take actions also prevents you from taking a bonus action.
And as you have observed, being incapacitated deprives you of your ability to take actions:
An incapacitated creature can't take actions or reactions.