IMHO.No issues with roaming, just say no 5G connections when roaming, no matter eight 4G or Singtel hi! 5G.
But 4G connections are good enough for roaming.
Interesting stuffs from AI
The China Issue: Even though your plan is a 5G SA plan, international roaming handshakes in mainland China can get tricky. If your iPhone has 5G Standalone turned ON, it tries to establish a direct connection with China's native SA core. However, if there is a tiny delay in your line authenticating back to Singtel's server in Singapore, the local Chinese tower (especially China Mobile) will reject the phone and drop you straight to 4G.
The China Issue: Even though your plan is a 5G SA plan, international roaming handshakes in mainland China can get tricky. If your iPhone has 5G Standalone turned ON, it tries to establish a direct connection with China's native SA core. However, if there is a tiny delay in your line authenticating back to Singtel's server in Singapore, the local Chinese tower (especially China Mobile) will reject the phone and drop you straight to 4G.
These are the basis on why I urgently need to change SIM card to true 5G SA. 5G NSA probably will work flawlessly based on the above. If that happens, there is no knowledge gained.