Hi En & Vladimir ---
Wow. Super nice. 10.35 grams is the correct weight. I presume you have taken the coin for XRF analysis, and the result came back platinum.
I brushed up my photoshop skills and made the attached side-by-side comparison of El niño's coin and a genuine coin (a proof) which sold for $10000 US dollars in a November 2021 auction. Check the details closely.
Something is clearly suspect about the strike of En's coin. The obverse (with eagle) is extremely weak, and the reverse looks a little mushy. If genuine, the obverse does not look like normal wear on the high points. Instead, it looks like a weak test strike, where the dies did not compress the planchet enough to form a sharp, raised pattern. You can see an example of this here:
En's eagle's left leg looks very similar to the genuine coin.
The genuine coin's strike is amazing. It is a proof coin, so a super-sharp strike is what you would expect. Two things bother me about the reverse: (1) the embellishment above the date looks different, and (2) the vertical spacing of the embellishment, date, and СПБ mint mark if off on En's coin compared to the genuine proof.
All in all, I cannot fully agree with Vladimir about authenticity. But I am not sure, and could easily be wrong. En's coin is close enough to genuine that it should go for authentication, grading, and encapsulation by PCGS, NGC, or ICG.
Hope it's real!!!