Canon EOS R5 Mark II Advanced User's Manual page 191

Caution
Shutter speeds you can set manually are in a range of 1/50.0–1/8192.0 sec.
Maximum sync speed in flash photography is limited to 1/181.0 sec. in shutter
modes other than [Electronic
In [Electronic ] shutter mode, maximum sync speed in flash photography is
limited to 1/128.0 sec. The following conditions limit maximum flash sync speed to
1/181.0 sec.
• With RF-S or EF-S lenses attached
• When set to [1.6x (crop)] (
Dark lenses may prevent correct display simulation.
Image display on the screen or in the viewfinder may differ from actual shooting
results. Take some test shots in advance.
].
)
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