Unfortunately, SmartThings made this more complicated when they introduced the “new” SmartThings Home Monitor (STHM) circa 2019.
Previously, integrations could directly control Smart Home Monitor, but the new system requires you to setup routines within the SmartThings mobile app to either connect Virtual Switches or Location Modes to your SmartThings Home Monitor State.
Check out the following article which also has a link to a YouTube video which demonstrates how you might do this.