Is SIM2 the primary SIM, should the 'No network' option only be selected in the SIM2 to SIM1 tab and not in the SIM1 to SIM2 tab? Hello,
Yes, this is correct. If SIM2 is your primary SIM, No Network option should be selected in SIM2 to SIM1 tab.
Checking the RUT950 LTE User Manual, this did not appear to contain/show, the 'switch back to primary SIM card' option/setting.
If you have selected SIM2 as your primary SIM, the option should appear in SIM1 to SIM2 tab.
The option is visible in the SIM-auto-switch2.JPG screenshot you have attached.