Does asking a guy if he has a girlfriend reveal my interest in him, or are guys even too slow to catch on to that?

Over the last few days on here, guys have been telling me that guys are slow to pick up on signs a girl is flirting. If I've learned correctly, just the one question alone won't signal she wants to go out with him, but that question along with her always trying to sit next to him, compliment him, ask him for advice, admire him, etc, he will see that question as flirting. But is that question (do you have a girlfriend) still too forward?

Does asking a guy if he has a girlfriend reveal my interest in him, or are guys even too slow to catch on to that?
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