Any university or national HPC system as I'd understand the term is multi-user.

There are also things like the extensive high energy physics WLCG compute federation, which is somewhat different, but can potentially be compromised quickly at large scale. For the original copy-fail we didn't want to drain our WLCG Alma9 cluster, or just kill all the jobs like the university HPC system. We got eBPF mitigation in place within a couple of hours, relieved the exploit signature wasn't in logs from the night before. That would have been done earlier if Proofpoint hadn't bounced the forwarded oss-security article as "contains malware"; sigh.