Solution
EOS R5/EOS R6’s [Movie Servo AF speed] is settable when [AF: Movie Servo AF] is set to [Enable]. Additionally, this function is only enabled when using the following lenses compatible with slow focus transition during movie shooting. (USM lenses released in 2009 or later and STM lenses are compatible with this function.)
RF35mm F1.8 MACRO IS STM
RF50mm F1.2 L USM
RF85mm F1.2 L USM
RF85mm F1.2 L USM DS
RF85mm F2 MACRO IS STM
RF600mm F11 IS STM
RF800mm F11 IS STM
RF15-35mm F2.8 L IS USM
RF24-70mm F2.8 L IS USM
RF24-105mm F4 L IS USM
RF24-240mm F4-6.3 IS USM
RF28-70mm F2 L USM
RF70-200mm F2.8 L IS USM
EF24mm f/2.8 IS USM
EF28mm f/2.8 IS USM
EF35mm f/1.4L II USM
EF35mm f/2 IS USM
EF40mm f/2.8 STM
EF50mm f/1.8 STM
EF85mm f/1.4L IS USM
EF100mm f/2.8L Macro IS USM
EF300mm f/2.8L IS II USM
EF400mm f/2.8L IS II USM
EF400mm f/2.8L IS III USM
EF400mm f/4 DO IS II USM
EF500mm f/4L IS II USM
EF600mm f/4L IS II USM
EF600mm f/4L IS III USM
EF8-15mm f/4L Fisheye USM
EF11-24mm f/4L USM
EF16-35mm f/2.8L III USM
EF16-35mm f/4L IS USM
EF24-105mm f/3.5-5.6 IS STM
EF24-105mm f/4L IS II USM
EF24-70mm f/2.8L II USM
EF24-70mm f/4L IS USM
EF70-200mm f/2.8L IS II USM
EF70-200mm f/2.8L IS III USM
EF70-200mm f/4L IS II USM
EF70-300mm f/4-5.6 IS II USM
EF70-300mm f/4-5.6L IS USM
EF100-400mm f/4.5-5.6L IS II USM
EF200-400mm f/4L IS USM Extender 1.4x
EF-S24mm f/2.8 STM
EF-S35mm f/2.8 Macro IS STM
EF-S10-18mm f/4.5-5.6 IS STM
EF-S15-85mm f/3.5-5.6 IS USM
EF-S18-55mm f/3.5-5.6 IS STM
EF-S18-55mm f/4-5.6 IS STM
EF-S18-135mm f/3.5-5.6 IS USM
EF-S18-135mm f/3.5-5.6 IS STM
EF-S55-250mm f/4-5.6 IS STM
NOTE