In airplane mode, both SIM(s) and wi-fi are disconnected. Is there a way to just disconnect the SIM(s) and keep wi-fi connected without root privilege?
In your Dialer / Phone app, enter
Turn off radio
Or use an app like Cell Radio ShutOff.
Note also that you can turn Wi-Fi back on during Airplane Mode (though it can definitely be annoying to have it turned off in the first place).