Russia has always been a fairly byzantine (heh) place, but this palace, why it was built, who built it, and who is going to live in it is a complete mystery.
My understanding is that Putin spends a good deal of time there (especially during the height of the pandemic in Russia). He has a room in that palace that is a mirror of the room in Moscow that he talks to the public from so it can appear he is at work in Moscow when he is really at his palace.