Your question does not make sense. A button has 2 states. If it can have values 0-100 it isn’t a button but a dimmer type (or “slider” in sidemap).
A roller shutter has a closure percentage state, that’s a 0-100 value and not a binary state (open/closed) and therefore cannot be converted.
If what you want is to display the word “open” or “close” in the UI use range transformations.
You need to do the rollercalibration (rc) according to the manual. Once this is done you can use the rollershutter item and send 0-100 commands to shellies/shellyswitch-/roller/0/command/pos and receive the status from shellies/shellyswitch-/roller/0/pos
Have a look at the api section of shelly, it’s really helpful https://shelly-api-docs.shelly.cloud/#shelly2-5-mqtt
Best regards Johannes