Yes, it is not recommended to use USD as the home currency for none-US users. Instead, select the home currency based on your location. You can browse these articles to know more about multicurrency in QuickBooks Online:
When you set up accounts, customer or vendor profiles, you'll have an additional field where you can set it for USD.
Here's how to create a USD account:
Here's how to create a USD customer profile:
Here's how to create a USD vendor profile:
You can always get back to us if you require additional help in setting up your multicurrency company. Have a great day!
If you are opening a QBO SG version, SGD will be your default home currency. You need to turn multi-currency feature on to set USD as the home currency.
As additional option, explore this payment service to deal with multi-currency transaction.
Hope it helps.