We scaled #Keycloak to 2_000 logins per second and 10_000 token refreshes per seconds on #AWS and it scaled linearly in our #loadtest! It performed just fine with the latest optimizations in the 26.4 release.
What load do you run on Keycloak? Do you host your own #IAM?
Spoiler: Most of the CPU is burned for crypto operations (password hashing, signatures, TLS)