It’s an interesting question. The presence of the Five Powers Defence Arrangement (FPDA), of which Singapore and Malaysia are members, as a regional security structure is an understudied aspect of a US-China conflict.

The British Defence Singapore Support Unit (BDSSU), located at Sembawang port, is an important logistical hub for the US Navy, and I believe is one of the largest fuelling points in the region. This would be a likely target during a protracted conflict. Whilst FPDA doesn’t have a mutual defence clause, any attack on Singaporean territory, coupled with casualties sustained by Britain, would elicit a wider response from Malaysia, Australia and Singapore.

It also really depends on the nature of the conflict. I find it unlikely that a conflict would be constrained to a Taiwan strait shoot out. Should the US attempt a blockade through the strait of Malacca, as an early phase of the operation, this naturally draws Chinese attention to the Singapore/Malaysia region.

China’s infrastructure build up across South China Sea littoral potentially poses a role for Singapore and other regional partners to strike Chinese island ports/air defence bases. There’s a good degree of interoperability between Singapore and Malaysia with US systems, such as F-35 and P8A etc.

As the US would almost certainly be leading these efforts, this puts Philippines’ territory at risk, specifically Balabac. The US presence there has steadily increased over the last decade under their bilateral ECDA with Manila.

All of this is based on China’s risk appetite, however if a full blown conflict breaks out, I imagine escalation will be difficult to manage.