To detect io_uring support, we call io_uring_get_probe() from liburing. This allows us to check what io_uring features are supported by the running kernel. It appears that some old kernels (the first few that supported io_uring) don’t actually support this kind of probing. So it is possible that your kernel has early io_uring support, but doesn’t being interrogated in this way. If that’s the case, then the only workaround at this time would be to update your kernel.
–Harris