Various people here like to point out that BSI for non-phone sensors is largely about marketing and not noticeable improvements, DxO has published their analysis of the R8/R6II sensor and agrees: DxOMark R8 test results.
Although neither ‘back-side-illuminated’ nor ‘stacked’ the 24.2 MP CMOS sensor in the Canon EOS R8 has similar performance characteristics to BSI sensors from rivals
Initially, though, the adoption of a conventional front-side illuminated 24.2 MP CMOS sensor appears to be a weak link. However, it’s clear, from our tests, the Canon EOS R8 sensor is capable of producing extremely high image quality. Indeed in terms of color depth and dynamic range, it is on par with the leading BSI-type CMOS sensors.