Greetings,
A Mod (acquaintance) of mine on the Canon community has told me all documented features are not official until the camera is released and links to the camera's documentation (manual) is linked from their support portal. The R52 manual is "unofficially" available but may not be 100% finalized. Do I think it's accurate now, probably.
Based on what's available now:
(unofficially)
You have to have 2 cards in the camera to capture still while shooting video
Single and continuous shooting will be possible
Images will be higher res than frame grabs from video
Movies are recorded in Full HD image quality (1920×1080). Still photos are captured as JPEGs with an aspect ratio of 16:9 (7680×4320).
Movies are recorded to card 1 and still photos to card 2.
Option off/on
View attachment 218518
Drive Mode is selectable too
View attachment 218517
Caveats
High speed
With [Set-up: System frequency] set to [59.94Hz:NTSC]: Continuous shooting at up to approx. 7.5 shots/sec. while pressed
With [Set-up: System frequency] set to [50.00Hz PAL]: Continuous shooting at up to approx. 6.2 shots/sec. while pressed
Low speed
With [Set-up: System frequency] set to [59.94Hz:NTSC]: Continuous shooting at up to approx. 5 shots/sec. while pressed
With [Set-up: System frequency] set to [50.00Hz PAL]: Continuous shooting at up to approx. 4.1 shots/sec. while pressed
Single shots
JPEG compression 1-10 is supported
More
Still photos cannot be captured during movie recording when RF-S or EF-S lenses are attached.
Some features are not available with [Shooting: Dual shooting (still&movie)] set to [On]. Some limitations also apply to movie recording sizes and anti-flicker shooting. Magnification from the point in focus is not available for still photos captured with this feature. Similarly, in-camera resizing, cropping, and upscaling are not available.
This is not 100% confirmed, but likely.