“7,737 tanks” “destroyed during Russia’s operation”
That number from February sounds like the old paper numbers, not the actual number of 900 usable tanks.
The Russian attack has resulted in about 450 Russian tanks going into Ukraine’s hands, but all this is a long, long way from whatever huge number of tanks Ukraine would have to have to meet your Russian source’s claim that almost 8,000 of them have been destroyed.
It's right there in the linked article.