Russians are Slavs, and the amount of Mongol they have in them is in the single-digits & comes from before the Mongol invasion.
View attachment 1070323
Genetically they correlate with other Europeans.
Belarus is more than 90% White, it's probably like 99.99% even excluding Jews & gypsies who aren't really "White" by most metrics.
I find a good way to actually asses a countries native population is by looking at the Military: I know Russia is big & very diverse, but I imagine most of the military volunteers would be actual Slav Russians, not some minor group such as Tatars.
From this pic, it seems they look distinctly White/European, though I can tell their facial-features & skull-shape apart from other groups on Europe.
Some Poles have that Nordic phenotype look, but many are mixed with other phenos/anthropological groups such as Alpinid & Dinaric.