Again, Dylan, that is simply not true. Below is a link to just one of many reports used by the IMF in their WEO update from January of this year. You can see for yourself some of the souces.

https://www.imf.org/en/Publications/WEO/Issues/2023/01/31/world-economic-outlook-update-january-2023

Below is a link to a selected list of the data used by the IMF in their assessments.

https://www.imf.org/external/np/ds/matrix.htm

I'm sure Russia lies about their data. I'm sure the IMF takes that into account as well. Russia does not exist in a vacuum. To fake out the IMF, all of Russia's international customers would also have to lie to the IMF, and consistently with Russia's lies.

TBH I don't trust the IMF either, but I expect them to err on the side of downgrading Russia, rather than making Russia look better than they really are.