He's been droning on and on about it since the 90s. He was totally triggered by NATO defending Kosovo against Serbia in the 90s, and getting locked up alone in the Kremlin during Covid lockdowns made him totally obsessed with this legacy.

This is not a secret. He posts about it in his presidential library, in these long-winded essays (feel free to go read them), or bores Tucker Carlson about the Russki Mir and the czars and Russia reclaiming its former glory, and how Ukraine and Belarus are actually Russia, and that Kjiv is the capital of Russia, etc.

Remember, he initially marched on Kyiv. He thought the Ukrainians would be grateful and the whole thing would be over in 3 weeks, and that Ukraine, Belarus, and Russia would happily unite, and now he refuses to admit that it was a dumb-ass idea and pull out his troops. If he admits that he fucked up, the vultures around him will throw him out of a window.

He's also just sort of an old fart. He doesn't use the Internet and gets his news in the bunker from people he hand-selected for their loyalty and their eagerness to make him happy.
The weirdest thing about his online voting video isn't even that it's an American PC running pirated Windows 11; it's that the monitor appears to have no cable. 🤷