They would probably like to, but NATO bases all around the world makes that hard. If the war ever ends it would be easier to make an assessment

For questions like this it is important to consider that imperialism is not something that a country can just do to another. Rather it is a phenomenon that has emerged from the womb a dying explicitly colonial epoch. The remnant tendrils of explicit colonialism in the global south were the foundation of the imperialistic arrangement we live in today where the USA exploited the utter devastation of WW2 to plant itself as the sole hegemon. Considering how USSR and China were devastated by WW2, it is hard to imagine that they would come out of it strongarming other countries into doing their bidding. They were on the back foot then and still are. They don't hold sway in any country's internal matters enough to be called imperial powers.

Another way of assessing that I like is considering how Prabhat and Utsa Patnaik (Indian Marxist economists) talk about imperialism in their two books. If you read Lenin's Imperialism, it almost comes off as a checklist. Radlibs in bad faith try to map this checklist onto Russia and China of today to claim they are imperialist. For example, if China builds a factory somewhere in Africa they say "China is exporting capital" and is therefore imperialist. The checklist is useful but it shouldn't draw attention from the most important thing, which is the consequences of the actions rather than the actions themselves. Patnaiks' conceptualisation is useful for this because they identify that imperialist actions and policies exist to drive down wages in the global south. For example, when IMF structural adjustments erode public services, working masses are driven to destitution and wages go down, making the target country profitable for "foreign investment". If you accept this definition, even if Russia and China take advantage of the preexisting balance of power to trade at favourable prices, they do not actively intervene to drive down wages and costs. Because of this I don't think China and Russia are imperialist.

Don't fall for the performances of shithead liberals who pretend to care about "imperialism" while ignoring the global north and south divide and pretend that everyone does a little bit of imperialism as a treat.

I recommend you some light reading, the excellent Michael Robert's(one of the leading modern Marxist economists) blog and this post on Chinese imperialism and by proxy also Russian imperialism

Now it is about China, but all the arguments apply to Russia since obviously Russia is extremely far behind Chinese economic development at this point. But even if this doesn't convince you it is at least important to understand, as he explains the actual economic definition of Imperialism. Every other definition from anyone that isn't a Marxist is just libshit, equivalent to "tankie". It is a meaningless term because they don't understand Lenin's definition and worse still don't even understand the modern context.

Also I don't know why but I'm convinced mainstream media uses the term as a proxy for "Empire building" which is why Russia(Putin just wanted the former Russian empire got it? lol lmao) was suddenly criticized for being imperialist even though their economy is not dependent on obvious imperialist characteristics i.e transfer of value from the global south. On the contrary, Russia is one of the biggest exporters of precious and valuable raw materials to the imperialist western powers.

Then there was the debate about the nature and causes of modern imperialism. Readers of this blog will know that Guglielmo Carchedi and I have published a paper on the economics of modern imperialism, in which we argue with empirical evidence that the economic core of modern imperialism is the unequal exchange of value (surplus value) through international trade (and capital flows) between the advanced capitalist economies and the rest of the world. It is the persistent and pervasive transfer of value to the advanced economies from the rest that best characterizes the former as imperialist.

Exploitation of the global south by the imperialist bloc is not mainly the result of ‘super-exploitation’ of the workers of the south or through the monopoly of markets and finance in the north; but through the redistribution of surplus value from the technologically backward economies to the technologically advanced, both through unequal exchange in trade and through the repatriation of profits, interest and rent by multi-nationals and banks.

Now our thesis was challenged by Charlie Post who also rejected the super exploitation and Leninist monopoly finance theories. He argued that using aggregate or average measures of the technological superiority of imperialist economies over those in the Global South failed to pick up sectors where the latter had already gained superiority. In particular, Charlie was arguing that China has become a leader in many sectors and so could not be considered just another exploited economy, but increasingly should be considered a future entrant into the imperialist bloc.

And yet in our paper, Carchedi and I had shown a large net transfer of surplus value from China to the imperialist bloc which we defined as the G7 plus a few other economies in the Global North. All have persistent and significant net value transfers from the rest of the world. On this definition, China (or for that matter, Russia) was not an imperialist state or economy. Moreover, no country since Japan and the US in the late 19th century has joined the imperialist club since 1915 when Lenin identified these imperialist nations – unless you consider tiny Taiwan or South Korea as entrants.

There is more and I definitely recommend you read the entire post and definitely the rest of the blog, you can use the search there if you're interested in certain topics.