Why does my boyfriend get defensive when I try to teach him something?

My 28f boyfriend 29m always gets defensive when I try to teach him about something he doesn't know. Does anyone else exercise this? So me and my boyfriend have been dating for almost 4 years now and we keep getting in disagreements about the most mundane topics. So everytime I tell him information about some random topic, he either doesn't believe me, has to do his research or says I'm talking at him not with him. I've asked him for ways for me to better explain information to him in his learning style but he just says either I don't know or it has to be hands on and debugging like coding. He's a software engineer. By the end of these conversations he ends up very defensive and ultimately learned nothing. Has anyone else dealt with this? It's exhausting and I feel dismissed honestly. Is this a red flag?

Why does my boyfriend get defensive when I try to teach him something?
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