If you lose interest in someone, tell them.
If you’re not looking for a relationship, tell the person you’re seeing.
If you’re thinking of ghosting someone, tell them.
If you can’t handle meeting up with someone after all, tell them.
If you’re terrible at responding to messages, tell people.
If you prefer talking in person to texting, tell people.
If you’re seeing several people at the same time, tell them.
If you’re looking for sex rather than dating, tell the person you’re seeing.
It is not difficult to be a decent and honest, open, communicative human being. Respect those whom you interact with and have relationships with by telling the truth instead of leading them on or being deceitful.
One exception: it is absolutely 100% okay to ghost someone who is abusive or who you fear may become abusive if you tell them you’re planning to leave.