Why does the video suggest avoiding the phrase “你好吗 (Nǐ hǎo ma)?” when greeting someone in Chinese?

It is not a natural way for native Chinese speakers to greet each other and it limits the possible responses to a simple yes or no.

To whom would you likely say “你吃饭了吗 (Nǐ chī fàn le ma)?” and what does it mean?

You would say it to family members or acquaintances, and it means “Have you eaten your meal?”

I can greet and simple conversation in Chinese.

1
Instead of saying “你好吗 Nǐ hǎo ma?” which translates to “you good or not?”, native Chinese speakers greet each other with “你好 Nǐ hǎo”, which means “Hi, hope you are well”.
2
To greet acquaintances, you can say “你吃饭了吗 Nǐ chī fàn le ma?”, which means “Have you eaten your meal?”, and respond with “吃过了 chī guò le” (I have eaten) or “还没呢 hái méi ne” (not yet).
3
To ask “How are you?” in Chinese, you can say “你今天怎么样 Nǐ jīntiān zěnme yàng?”, and to ask “How have you been?” you can say “你最近怎么样 Nǐ zuìjìn zěnme yàng?”, responding with “还好 hái hǎo” (so far so good) or “我很忙 wǒ hěn máng” (I am busy).