Your definition of imperialism is taken from an imperialist source, interested in obfuscating it.

Here, some reading: https://arkansasworker.com/is-russia-imperialist/

And how the entire war came to be:

https://archive.ph/2ppei

https://www.moonofalabama.org/2023/02/the-buildup-to-war-in-ukraine-february-15-2022.html

So, in theory, I don't know a lot about modern day Russia. They are capitalist, and maybe they are practicing some imperialism, or would if the had the chance. But my focus has been elsewhere.

But I have learne a bit about this current conflict, and it goes back to 2014. There's more reasons for Russia to get involved. Such as Ukraine shelling their own people who didn't support the wests military coup, and those people being Russia-friendly, speak Russian, and possibly wanting to leave for Russia. There's a lot more nuance. I recommend checking more info out.

Now me personally, I don't care about Russia or Putin. I'm not a fan of the country, but I get why China, Africa, and others might partner with them. The wests military coups to oppress governments into handing over raw materials for poverty wages is just too consistent. For a modern example: niger and uranium and gold exports to France.

Everyone not in the imperial core have come to realize that NATO is not their friends, they are their oppressors. Partnering with Russia is a strategic choice.

My 2c, I don't represent all opinions here of course.