I don’t know the exact utilization, but most large supercomputers that I’m familiar with have very high utilization, like around 90%. The Slurm/PBS queue times can sometimes be measured in days.

On a node-level, usually these are aiming for around 90-95% allocated. Note that, compared to most "cloud" applications, that usually involves a number of tricks at the system scheduling level to achieve.

At some point, in order to concurrently allocate a 1000-node job, all 1000 nodes will need to be briefly unoccupied ahead of that, and that can introduce some unavoidable gaps in system usage. Tuning in the "backfill" scheduling part of the workload manager can help reduce that, and a healthy mix of smaller single-node short-duration work alongside bigger multi-day multi-thousand-node jobs helps keep the machine busy.