In the updated Roaming Partner List (PDF file) updated on 1 Feb 2023, SIMBA is now able to roam on Digi network in Malaysia. This is good news as SIMBA users are better covered by two 4G networks.
This reason is because Celcom and Digi have merged into celcomdigi. That is probably the reason why subscribers can now roam on either network.
Both existing Celcom and Digi operates on bands 1,3,7 and 8.
Do take note that you can dial direct with VoLTE enabled when roaming on Celcom. If you are connected to Digi, you will need to run the Simba Voice app to make and receive calls.