Here's what it says at Canon Europe:
https://www.canon-europe.com/pro/infobank/usm-stm-lens-technology/
Like other USM units, the Nano USM motor has an elastic metal body, a ceramic voltage element and a drive unit. Sending current and varying the voltage applied to the ceramic elements creates two types of vibrations, which enable the motor to precisely control the speed and direction of the drive unit. However, the movement is linear rather than rotational – the lens focus elements are driven by a rack, with guide bars to control the forward and backwards movement. The outcome is smooth focusing with fine control over speed and near-silent operation.
Launched in October 2019, the
RF 70-200mm F2.8L IS USM is the first lens to feature Dual Nano USM technology. It has two Nano USM motors, each driving different lens groups, working together to produce faster, more efficient focusing.