This effectively looks the same, but the factory and expression are more general, and this can be ported to an AdwComboRow almost directly (literally just s/GtkDropDown/AdwComboRow//g and s/gtk_drop_down/adw_combo_row/g), if that's the route we end up with for the account settings.

Opened a new account dialog, changed protocols and saw that things changed a bit, also tried on an existing account.