Hi,
For preventing the creation of lead, please switch off the option “Create leads for event registrations” in the Website and form tab of the Event form.

So that no corresponding lead is created after the event is registered.
But I don't know what data you mention here other than LEAD.
For example, if the contact for registration does not exist, the contact will be created anyway, as it is a required field in the Event Registration entity.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya