I just found this out for the MultiTimer app. With the System Sounds turned on in Accessibility on my iPhone in iOS 14.2, a timer started on my iPhone will ring in my HA’s. But if I start the same timer on the watch, I get a much fainter, easier to overlook ding-ding on the watch. What I’d like even more, since the timers can be named, would be if the ding-ding could be in my ears and the app would also announce the name of the timer that went off. I’ll try the developer.
Edit_Update: I did find an (impractical) way to get watch notifications sent to the iPhone (and thus to my HA’s). If you turn off Wrist Detection, then when the MultiTimer goes off on the watch, the notification goes to the phone and sounds in my HA’s. But when you turn off Wrist Detection, one disables a whole bunch of other useful functions, including activity tracking and heart monitoring, fall detection, etc. Source of idea: iOS: Fixing iPhone No Notifications Sound When Locked - miapple.me.