I have not paid attention to COVID-19 recently and I recall that Chinese vaccines were problematic against Omicron.
If it is so efficient then why the hell they have this security theater in China?
Not sure why you call it "security theater". The lockdowns in China work, even against Omicron, even if it has become way more difficult. Shenyang, Guilin, Shenzhen, Guangzhou all defeated omicron without the Shanghai mess.
As for why they don't push vaccines more, that I don't know. Possibly because they are more cautious about vaccine side effects than we are. As I said, doctors in China recommend against getting vaccinated if you have other health problems. The same elderly in the Netherlands would just get a recommendation to get vaccinated because "vaccines are very safe", as we are officially told here.
A similar notion existed in Taiwan until they got overwhelmed by Omicron. Lockdowns worked and they were able to keep COVID out of the island, so people weren't interested in vaccines hence low vaccination rates.
Western societies view lockdowns as draconian human rights violations, and don't take COVID very seriously relative to "freedom", but not all societies look at things that way. Chinese people are very afraid of COVID, much more so than westerners, and see lockdowns as an inconvenient but absolutely neccessary measure. Chinese society values responsibility more than freedom.