he majority of Canon’s EF and EF-S T ‘USM’ (Ultrasonic Motor) lenses for EOS DSLRs have a physical connection between the focusing ring and the focusing optics. There are exceptions though, such as the EF 85mm f/1.2L II USM and the EF-S 18-135mm f/3.5-5.6 IS USM, both of which utilize electronic manual focusing instead. Electronic focusing is a focus-by-wire system, where the camera adjusts the focusing distance via a motor when you turn the focusing ring. Lenses that are designed for the mirrorless EOS R System, as well as DSLR lenses that are equipped with an ‘STM’ (Stepping Motor) instead of a USM, also only offer electronic focusing.
One of the potential drawbacks with an electronic focusing ring is that isn’t as tactile; there can be a lag between the ring being rotated and the focus distance changing. It can be very subtle, but it’s typically more noticeable on STM lenses than those that are fitted with the newer Nano USM motors.