In legacy (old) quizzes, the answer is to not use question groups.
If your items are in a bank, then find the ones you want from the bank and include them into the quiz rather than linking them to a bank. When adding them, choose not to put them into a group. Then, you can reorder them by dragging and dropping the questions. Here's the relevant lesson from the Canvas Instructor Guide: How do I create a quiz by finding questions in a question bank?
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