ShiftNav works without issue with GeneratePress in my tests, and I’ve never had a user report such an issue, though many use GeneratePress with ShiftNav successfully.
Sounds like you encountered some other issue and may have misdiagnosed the problem.
If you encounter a specific issue, you’re welcome to submit a support ticket and let us know what the issue is, and we can help you assess it.
Not explaining the issue or thoroughly examining it before leaving a review doesn’t help anyone, unfortunately. And even if there were an incompatibility with a specific theme, that does not necessarily warrant a 1-star review, without knowing where the actual issue lies.