I like the processing IDE, but i hate that my tabs are along the top. Is there any way to change the layout to have the tabs in a sidebar like a normal IDE?
Not the way you want. You can adjust the theme or even create your own theme with a bit of studying how to.
But you can also integrate processing into other editors like ie. vscode (including code completion,run sketch,etc). There are several howto’s out there. Just Google for it and follow the steps if you like…