I am have been unable to get sim slot #2 to work. Both sims work fine in slot#1.
I finally discovered to they to get the Sim#2 active (Turn off "Default Sim" under Network--> Mobile->Sim Card Settings, then reboot the entire device)
When the Network interface for SIM #2 is active, the following error is generated(Cannot read properties of undefined (reading '.name')) when trying to change the settings.
This error is not generated doing the same operation on Interface for SIM #1.
The error is not generated if SIM#1 is selected for the new interface.
I did managed to save the new interface for SIM#1 then change it afterwards but it then threw this error (COULD NOT REGAIN ACCESS TO THE DEVICE AFTER APPLYING THE CONFIGURATION CHANGES)
The manual is not at all clear on the procedure for changing which sim is being used. There are several questions on this forum about it where the answers are not clear either.
I think there is a bug here and I think the documentation needs improving around how the second sim slot should be activated.
Brave browser(Version 1.31.88 Chromium: 95.0.4638.69 (Official Build) (x86_64))
After a full factory reset and further testing I am able to get the sim to change reasonably quickly now just by toggling the "default sim" switch. I have been able to get the second sim in slot #2 to connect. But I suspect there is a bug in saving info for the second sim slot that then causes issues. Maybe saving changes to that interface while it is active? Not sure.
Please let me know if you need any further info. Happy to help.