@kriol
I'm not familiar with Feedback Fruits (FF) in particular, so I'll address this from a general perspective.
The answer to the first part (why does it appear in the menu) is because Feedback Fruits decided to add that functionality. Canvas supports a lot of areas that external tools can be placed. The module group menu placement sounds like what you are describing. You can also add LTI 1.3 tools to the plus button to add a module item. In Canvas, you can often get to things in multiple ways. Your workflow of using the + button may not be the same as someone else, who uses the module menu. I can understand why FF might want to include it in different places.
You may be able to go to your Course Settings and select the Apps tab. Then click on "View App Configurations". Find the Feedback Fruits tool and click on the information button to see all of the placements. You won't be able to change the placement, but you can see all the places it is set to show up.
Placements are set when the tool is added and often tools like to give themselves as much visibility as possible. We've had many tools that add themselves to the course menu and set themselves to be visible so it shows up on every course, even though a very few courses may need it (example, a math homework tool that shows up in history or foreign language courses).
There are ways to change that, but your local Canvas administrator is the one that needs to take care of that as it is installed for your entire institution. In my example, when I installed that math homework tool, I waited until the middle of the night while we were on a break. As soon as it was installed, I sent the changes to change the default visibility, so it only appeared to people for about a minute. If I, as an admin, hadn't changed that setting, then every instructor would have had to go into their course settings > navigation tab and remove it.
Your Canvas admin may want the added visibility because you're paying for the FF tool and they would want it to be used. I agree that it doesn't fit with the other items under the menu group menu, but those are Canvas items and how Canvas decided to organize things. Ultimately, Canvas gave external tools the ability to add things there and FF chose to take them up on it. Unless companies get feedback from their customers that it is wrong, they're going to keep doing things like that.
As for why the X doesn't close the window, that could be a bug. Ideally, there would be a Cancel and Save button at the bottom, along with the X at the top. It's impossible for me to say whether the problem is with Canvas or FF or someone else completely. If FF added an eventListener to the X to make sure something happens when people close the dialog and there was a problem with their software and they never passed that event on to Canvas when they were done with it, it would appear the X was broken.
For sites that have problems with their JavaScript that result in an error, functionality stops working. My math homework tool had one of those where it assumed an object was there when it wasn't. JavaScript threw an error and I couldn't do what I needed to do. That was something I had to reach out to the company to fix. I told them what was happening, what line of the source code was being called when the error happened, and what I thought the solution was, although realizing it was probably something else and this was just a symptom. They quickly responded and fixed the issue.
Things like that are hard to diagnose in a forum like this where we don't have access to the system having the problem. The X works for Canvas-native functionality, so it may be on the FF end. It's possible that your institution has installed some custom JavaScript that is breaking things as well. If someone at your institution is capable of using the browser's developer tools to look for error messages, you can have them try to diagnose the issue. In the meantime, you may get more out of FF support than Canvas support. But this is something you can talk with your local Canvas support about trying to figure out and they may be able to determine where to send the support ticket. About all we can do here is give general advice that fixes a lot of things (clear the browser cookies, restart the computer, try a different browser, try incognito mode, etc.).
