CrYpT999
Yes it works for me with data SIM in roaming. I tested it by first selecting an forbidden network for the primary SIM. Then I activated the second data SIM and selected it for mobile data. I selected the first SIM for calls and texts.
I noticed that if you select only the primary SIM (without a network) for calls, texts, and mobile data, but activate the second SIM with auto data switch enabled, the network switches to the data SIM, but backup calling isn't activated. Even when you then select the data SIM for mobile data again, backup calling still doesn't activate; it only works after disabling and then re-enabling auto data switch.