It’s from Advanced Canvas plugin. You can get it from “Community plugins”.
- After being enabled, you can change the line shape by clicking on it, it would be a menu.
- Click the icon at the right corner of the menu.
- Select which shape you want.
If you want to set a default line shape:
- Go to “Advanced Canvas” settings.
- Go to “Edges styling” section (actually, the connector lines of Obsidian canvas are known as “Edges”)
- Open “Default edge style attributes”, select “Pathfinding Method”.
This video gives a better explanation.