If by calibrated, you strictly mean with a standardized device, yes. But, to within a very practical, useful, real-world usage degree of accuracy, Viggo, the EVF and the LCD of the R5/R6 can be calibrated by eye. Simply work with the brightness controls, comparing them to correct exposures, and perhaps tweaking the Picture Style settings (in-camera and with Canon's Picture Style Editor), and you can get VERY close to SPOT ON WYSIWYG.Difference is, a monitor can and should be calibrated, the camera screen can’t.
Takes some patience and time, but, in my opinion, the investment is important and rewarding.
And I would say that the metering of the R5/R6 is indeed "proper." Include the Histogram with the EVF representation, and correct exposures are solidly consistent in all types of lighting scenarios. (The only purpose I see for an external meter, with my photography at this time, is for flash. My Paul C. Buff Cyber Commander's integrated flash meter is just as accurate in practical terms as my Kenko light/flash meter. Yes, there must be more precise meters for more money, but, in practical use, my exposures are, as stated, consistently correct. Why worry about more than this?