Sony Venice 6k vs Alexa LF 4.5k - Camera

Sure there are charts that can be shot to measure recorded line resolution, same as for measuring sharpness of lenses. But I've never shot such a test, never had needed to. If I ever did, it would only be to satisfy some intellectual curiosity, it wouldn't have much practical value.
I'm sure both cameras produce images of similar resolution that is adequate for most any application.
6K and 4.5K just refer to the number of horizontal photosites in the sensor, and the corresponding file size of the raw image being recorded -- not the recorded amount of measurable detail. The design of the optical low pass filter will have an effect on measurable detail, as well as the lens used, and the recording format (if not raw.) And even the raw conversion software may have an effect.
The only way it might matter is if you were working on a Netflix series with a mandate to shoot on a 4K camera and you planned on heavy cropping in order to do a lot of image stabilization and reframing, and even then, it would mainly matter to Netflix if you had to stay at 4K or higher. In that case, you'd have more ability (by their rules) to crop if you started with a 6K or 8K recording.

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