Officially, but not operationally. Where do you think does the US navy carrier strike group docked to resupply in the South China Sea if not in Changi naval base, Singapore. Malaysia has their Butterworth AB operates by the RAAF, not to mention that both Singapore and Malaysia are FPDA members.
Thailand is cozying with China and probably the only country of significance in ASEAN and Asia Pacific as a whole that doesn't share the fear of a militarily dominant China. But their military still have a significant tie with Washington.
Vietnam is officially neutral, but continue to be a headache for China's claim in the South China sea.
Philippines is now moving away from Duterte era honeymoon with China, with Marcos Jr in power. They're already earmarked $35B for a new military buildup, increased military exercise with the U.S. and is involved in multiple high level diplomatic incident with China, notably on Twitter/ X .
Like I said, every country has it's motives, some are more alarmist than the other, Australia for example despite being much further away Indonesia to the SCS, displayed a more aggressive postures than Indonesia, Philippines,Vietnam. But most of them does share a concern of a militarily dominant China and each has done their own preparations, some in conjunction with each other