1 ACCEPTED SOLUTION
In anticipation of your reply that you have been using EF-S lenses, there is an issue with using those lenses, which are designed for an APS-C camera, as they behave on a Full-Frame one like your EOS R.
In the DSLR platform you could not put those lenses on a FF body, as an EF-S lens projects too close to the sensor and fouls the mirror. While there is no mirror on the EOS R, the image that is projected from an EF-S lens is still going to be the size of an APS-C sensor and thus will not use the whole area of the FF sensor. This causes the area covered to be reduced from 30MP to just under 12MP, which is what you are experiencing.
See P610 in the Advanced User Guide and refer to the column under 1.6 crop for the values you are experiencing.
There is no work around this except to use EF or RF (not RF-S) lenses if you want to use the full area of the R sensor.
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