It is my understanding that it is preferred that your tenant should be registered in a country where you have a registered business address. Does your business have a registered address in Singapore? If not, how are you paying for the subscription? your CSP provider would have likely asked for your registered address in that country.
I see Cambodia is listed as an available country here: https://www.microsoft.com/en-gb/microsoft-365/business/international-availability
Unless you are referring to Azure Regions where you can provision resources? In which case any region is fine, specifically Southeast Asia.
Whereabouts are you seeing this problem?