I am running into this same issue and believe it may be a bug in the beta (or I'm clearly doing something wrong).
I am following along the WWDC video and noticed that if I remove LiveActivityIntent & only keep SetValueIntent, my toggle state will be properly updated. However, I then get hit with a Target does not include NSSupportsLiveActivities plist key but I have added the key to both App Target and Extension Target.
When I re-add LiveActivityIntent, my live activity begins correctly but my ControlWidgetToggle state does not stay "on".
If this is not a bug, any advice from the Apple team would be appreciated. Thank you!