The Aisin transmissions used in Lexus cars are very well protected against possible damage, there is a temperature sensor unit for the transmission oil which via the ECU limits the full scope of the gearbox until the fluid is up to its normal working temperature.
During this time the hydraulic pressure is held at a reduced level protecting the seals, probably the cause of your concerns and the transmission will not go into top gear.
Nothing to worry about just Japanese self preservation :)
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