Blue dot in text

Is the blue dot a setting? Can it be turned off and on? Also is it on every generation or just newer ones?

The blue dot is to signify if you have read a message, not if the person who you sent the message to has read the message. It is possible they had read your message that you sent and replied to it, but you have not read the reply.

The blue dot should go away after you have read the message or reply.

I have a blue dot next to a text. It does nothing when I tap on it. I am also unable to answer text. It is OK now.