using only one sim :
sim 1 active,
and phone call, message, and data are set on sim 1
data works, phone call works, but now an then i lost...
Don't realy understand what you mean by "sub"
using only one phone chip,
everything is set by default using 2g/3g/4g(auto)
with roaming on
i'am in France,
experiencing trouble with network connectivity on my Oneplus Nord
Often i have the "mobile network not available"...