On Catalyst, it is possible in newer Firmware versions. If Transition mode is configured, it enables WPA3-Transition on 2.4 and 5, but WPA3-only on 6 GHz.
EDIT: I just looked; the same is valid for Mist. This makes me think it could be common outside of the Meraki world.
EDIT2: I still would prefer a separate SSID in most cases as I am not a friend of any transition mode.
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