This is the broadest yet most specific definition of a theme. And yes, ‘any’ means ‘any’.

Themes don’t necessarily have to be intentional, as themes can end up being emergent without the author intending it. Though this shouldn’t be confused with Death of the Author.
Though when people (amateur YouTube critics) talk about themes, they tend to not talk about the emergent ones but the ones that are intentionally placed in a film.

Examples of the type that are intentional would be Do Androids Dream of Electric Sheep? in Blade Runner and “Life, uh, finds a way” in Jurassic Park. Coincidentally, neither of those films explore those specific themes properly. Jurassic Park, in fact, has a different emergent theme: showing the consequences of Zoo mismanagement.

Death Note is probably the pre-eminent example of a work that has an emergent theme: as it sorta, kinda, not really explores the question of what justice is, embodied by Kira or L.
Emergent themes are usually a side-effect of good storytelling – though this is not something that should be relied upon as a guarantee and, further, the presence of an emergent theme isn’t necessarily an indicator of good storytelling.
An emergent theme is also a side-effect of bad storytelling, since a poorly-written plot might have a radically different theme from the intended theme.

Exploring the them is not the same as mentioning it. Exploring involves raising the idea/question and then showing it play out in real time.

Using the example above of Jurassic Park’s Zoo Mismanagement theme: it shows the consequences of mismanagement, as well as the specific things that contribute to that mismanagement.
To give specifics (though not too many!) on those contributing factors: the entire computer system is managed by one guy, who isn’t paid enough; park employees don’t know enough about the animals they’re meant to take care of to actually take care of them; many of the enclosures are too small; they don’t realize they can sedate dangerous animals before moving them.
Now for consequences: the park’s computer system is hijacked, resulting in a blackout; animals become sick; animals start escaping the second they have the opportunity to; a man was eaten by Raptors; many people died.

In contrast, mentioning a theme generally means that you point at it and go “Do Androids Dream of Electric Sheep?” and then calling it a day. You don’t really show the specifics of what contributes to that theme, or show consequences…or really do anything.
Viewers can also mis-identify themes just by assuming that exploring is the same thing as mentioning.