In my external keyboard only, the tilde/backtick key produces section/plus-minus symbols. On the internal keyboard, they work fine. (Hebrew/English keyboards).
This problem has been discussed 1 2. However, the solutions do not work. I tried re-recognizing the keyboard in Settings and defining mappings in Karabiner as in the screenshot below, but these do not fix the problem.
Best Answer
You can probably find backpack/tilde on the topmost leftmost key instead of where you expect it.
Here is a custom layout made with Ukelele which may put it back where you want it.