So, in a game I played in it was ruled that the incapacitated only prevented Actions and Reactions and didn't prevent Bonus Actions or the boss monster's Legendary Actions. I always interpreted it as "prevents all types of actions." Thoughts?

From PHB Chapter 9: Combat, on the section for Bonus Actions we find the last sentence:

You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action.

So, yes. being deprived of your actions from being incapacitated deprives you also of bonus actions.

Oh and re:legendary actions, the monster manual introduction, where it discusses legendary actions says:

It can forgo using them, and it can’t use them while incapacitated or otherwise unable to take actions.

and re:lair actions it also says:

It can’t do so while incapacitated or otherwise unable to take actions.

So if you are deprived actions you are also deprived lair and legendary actions.

It certainly would be easier in play if the condition told you these things. But I can see why the designers might have chose to do it this way: the conditions only affect general abilities (everyone has actions) and so exceptions (bonus actions are only available to some creatures) have to have their own rules when it comes to these things.

Yeah, it is annoying when multiple related rules are in different places. It is kind of unavoidable though.

Yeah, it sure does. Thanks for the clarification, y'all!