It’s not “me” who’s saying this. This is just standard Chinese narrative on why the PRC sided with the US to destroy the USSR

So, you uncritically believe the PRC on why destroying its allies was good, and choose to regurgitate that narrative when it's obviously ass?

You also need to understand that Sino-Soviet relationship had always been tense

Not exactly a reason to actively help NATO take down your allies and make NATO's positions in the world stronger.

It wasn’t just the Russian Empire getting involved in the Eight-Nation Alliances to carve out the Qing Empire and annexed the Northeast, but also when Stalin insisted on the independence of outer Mongolia to assert its influence in Central Asia, his insistent on using Port Arthur (Lushunkou) as “shared” Sino-Soviet naval base (i.e. stationing Soviet troops in Chinese province), retaining the control of Chinese Eastern Railway, and the refusal to return Vladivostok (Haishenwei) to Chinese sovereignty.

Sure. And you claim that this is a good reason to destroy your major ally and shoot yourself in the foot?
Also, you talk about realpolitik, and now you bring up past offences when realpolitik in large part revolves around ignoring grudges. You are clearly not thinking about this in any sort of rigorous manner, but are just trying to invent a way to present the relevant actions of the PRC as somehow good.

Some of these major issues got settled after the Mao-Stalin meeting in 1949-50 during the “honeymoon” period but the threat of “Soviet imperialism” has always been latent

By your logic, the USSR should have destroyed the Chinese communists during the civil war and handed China over to anti-communists. That would have been a very swell move for both the USSR and the workers of the world, wouldn't it?

After Stalin died, the Soviets went mask off with their intentions and started to threaten Chinese national sovereignty

'Went mask-off'? You mean the state that was assisting multiple national liberation movements in the world in Asia, Africa, and the Americas at the time was 'going mask off'?
You also have not presented any sort of evidence for the USSR seriously threatening the PRC's sovereignty.
Also, are we to believe that NATO did not threaten the PRC's sovereignty?

It’s a lot more nuanced than people are making it out to be

You are not doing a good job of presenting this supposed nuance, and have already contradicted your claim that 'this is just realpolitik' when you brought up then-past offences of the USSR and, even less relevantly, of the Russian Empire (and forgot to bring up the offences of the western powers like the British Empire, including the fact that they were and are actually trying to threaten the PRC's sovereignty).