Thank you for your comment.
This is a subjective choice in some way.
Ruby does not require you to do that, as you probably know, but I want to say this out loud to anyone that might read this.
Rails with .erb, for example, allows anyone to choose how much they want to write in Ruby and how much they want to write in HTML, with the majority being HTML/CSS.
In my case, I am a backend engineer, so when I think about Frontend work, I want to generate it automatically. I think about frontend in pieces that I want to be stable, and then I want to compose them in what is needed. Thus I, for example, like a lot Phlex and ViewComponent, but I understand that this is a personal choice that I have due to the way I see the interface.
The option to go more toward HTML or to try to use Ruby to write FE components has more to do with a mental model of how we see a web app built. Of course, I think there are more pros than cons in choosing to build the UI composable by using objects, but in this specific case, it does not matter if that code is copied in all files or put in a shared partial and included in all files. It is small enough to allow almost all choices.
In my case, I wanted it to be a helper to make sure that any other developer that wants a separator with 3 dots will use this one and not create a slightly different flavor. So, I put this into a helper because the project doesn't have ViewComponent or anything else.