What is shutter sw?

It is recommended to use a shutter switch because mechanically it does not allow simultaneous switching of both channels. Although the Shelly 2, 2.5 or Plus2PM has this protection on the software side, if the Shelly is in relay mode for whatever reason, normal buttons/switches could damage the roller shutter motors.

You don't have to worry, I don't know of any case where the Shelly 2.5 destroyed a motor in shutter mode. This is purely a recommendation with the roller shutter switch, but not a must. As a rule, there are roller shutter switches from all common switch programs from the respective manufacturers.