In Slack/Discord/Element/Gitter each part of the message is arranged on the left: Avatar, username, reactions, the text of the message itself (most texts are short). But each message has a menu: "Edit/Delete/Forward/..." and this menu is placed in the upper right corner of the message in Slack/Discord/Element/Grid (or is hidden on mouse-over).
The problem with placing the menu on the right side is that you have to mouse-over all the way through the message to the right part of the screen, with the risk of hitting another message, so you have to pay attention to which message is highlighted (by mouse-over event) - the right one or the wrong one?
So you have to remember and follow the horizontal bar. When you mouse over the menu button, you have no idea what message is associated with that menu button until you slide your eyes to the left and read the text while the mouse pointer stays on the menu button. They also do not place likes/reactions in the right part of the message, why is the menu icon like this?
Why do not they somehow place the message menu on the left side where ALL the elements of the message are? That way you can see the message related to the menu icon and the menu icon at the same time? Examples (3 dots in each example are a message menu):