No going to happen. Instead of looking at the effect of such blokade on China's trades, we shall look at the importance of Malacca Straits and South China sea to Singapore.
Singapore 's import and exports and transhipment trades go through Malacca Straits and South China sea, is in fact closedly related to China's trade. Moreover these import and export and transhipment was reported at 322% (Three Hundred and Twenty Two %) of Sigapore's GDP in 2024. I don't know if there is any other country that depend on so much of a straits shipping lane on their GDP other than Singapore.
Blocking China's shipping in Malacca straits will kill practically every industry sectors in Singapore, from manufacturing, shipping, banking, insurance, shipyard repairs and mantenance etc. It is a suicide act of stupidity.
Morever, the control of Malacca Straits is jointly undertaken by binding agreement, by 3 countries, Singapore, Malaysia and Indonesia. Singapore's unilateral action, if taken, will invite excuses fro Malaysia and Indonesia to attack the island nation. And China will joint these two countries.
It is not a lost-lost situation, it is an extinction for Singapore, they will be erased from the map as a nation. Singapore is a small country of 719 Sq KM, or 1/47 the size of Hainan island, they have no area to fall back during an attack.
So, no, it is not going to happen.
Yes.
And if you read Kaplan's book (Asia's Cauldron), Singaporean government thinking is that freedom of seaborne commercial navigation is an existential matter for Singapore's survival.
If anyone starts blockading the Malacca Straits, it is in Singapore's interest to break that blockade.
And note that it is the US which keeps going on about a Malacca blockade, whilst China will always want to keep the Malacca Straits open.
China-ASEAN trade is also intertwined, so China and ASEAN in general have an interest in keeping the Malacca Straits open.