The Chinese just want to have pro-China candidates, not necessarily pro-CCP candidates.
Yeah, but we're talking about local HK elections, not national elections. "Chinese" people living across the PRC don't get to decide. Do people living in Beijing get to decide who can be a candidate for the Mayor of Shanghai? No, they don't.
Also, for the CCP, pro-China is the same as pro-CCP. In their minds it's not possible to be pro-China yet a critic of CCP policy. For example, note Xu Zhangrun and Ren Zhiqiang. (Unless you want to say they're good Chinese people who have been unjustly treated.)
Of course, traitors, separatists and people under foreign influence are not allowed to be nominated
Uhuh, but by themselves those are vague terms.
You should have clear and unambiguous reasons to as to why someone cannot be nominated for office. For example, they're too young - you set a minimum age. Or past criminal behaviour - you could say a candidate could not have been convicted for treason, sent to jail for more than 12 months for a crime, etc. But to say something like you can't be under "foreign influence" is completely subjective. There's no way to assess that in an objective way, because it's a matter of personal opinion.
If what the CCP had wanted was normal in the vast majority of countries, I would understand. However, I'm struggling to think of democratic countries where in order to stand for election you first have to pass a nominating committee that is controlled by the ruling party.