An update:
It is regulation that you don’t get a migration card if you travelled from Belarus to Russia.
So, at entry: quick entry without migration card.
At exit: quick exit without migration card.
No questions raised.
At hotel check-in in Moscow: juat told them that I am coming from Belarus and no issue at all.
Even in internal flight from St. Peteraburg to Moscow no issue at all.
The hotel in Saint Petersburg, just didn’t know that you dont get migration card if you are coming from Belarus, so they took me to ministery of interior office, and the government told them that I don’t need one, and I won’t face any issues with pssport control upon leaving the country (and they were 100% correct).
The only concern was for the hotel: how the hotel in st.petersburg would register me without migration card?
The hotel in Moscow didnt raise such concern which tells me that they have more experience than the one in Saint.
Long story short: you don’t need migration card travelling from Belarus to Russia.