Heya man, glad to see you're still creating. A brilliant guy on Youtube by the name of "Michael Games" posted an interesting video today on collisions called: "Your Bullets Are Missing Collisions (Here's Why)". Thought it might re-ignite your passion for the project. Cheers!
Heh, even after a couple of years I still feel like a noob. The dev team is so productive that simply keeping up with all the new update goodies feels like treading water sometimes. By the way, I think JOLT physics is now built in, but you may have to enable it in your project settings. Note, if you decide all of the "Michael Games" solutions are too involved or math intensive, you can just crank up your physics loop settings to 120 per second instead of 60 on your current project. Since JOLT seems to be designed for thousands of hard body physics objects at once, it might be overkill for pinball (like killing a gnat with a bazooka). The "Michael Games" solution with a few simple character bodies calling internally scripted physics processes (for balls, flippers, and possibly *bumpers) might give you much better performance, dunno. (*Alternatively, static bumper interaction physics could be a small function in the pinball script. e.g. Pinball detects the bumper area2D >> pinball alters it's own trajectory and tells the parent of bumper area2d to flash and jiggle.) Apologies for the info dump. Best of luck to you!