I struggled for some time as well. Just follow what they explain in their video from WWDC 2024 "Bring your Live Activity to Apple Watch". There they explain that you need a key: WKSupportsLiveActivityLaunchAttributeTypes as written above. But setting it in the Info.plist is not enough for my project. It only works if you: go to your watch target -> build settings. Select "all". Under "Info.plist Values" you will find the key: "Supports Launch for Live Activity Attribute Types". To add an empty value there did not work for me. So, as in the video, I added my Attributes in my case called "NameofmyappAttributes". Having this set, now tapping on the LA on the watch starts the watch app. Took me many hours to figure that out.

Could somebody from Apple please have a look?