Some years later, I have another Xperia 10 II Dual SIM with Sailfish 4.6 (Sauna). Now Bluetooth works better - well done Jolla!
BankID seems more complicated these days. Found another thread about that: Swedish Bank-ID/Swish - #91 by eson
However, a peculiar thing was that when I put a second (Norwegian) SIM card in the phone here in Sweden, suddenly none of the SIM cards seemed to register on the network (not even SIM1, which is Swedish, and worked before). After I allowed roaming for SIM2, both SIM cards work as they should.