I use Siri fairly frequently for setting timers, controlling my smart home and the like, but for me where it falls down is really understanding natural language. Personally I found that google assistant was way way ahead of siri in this regard. I could ask it to do something and it would just understand what I want.

One issue I frequently have with siri is that commands that work one day suddenly don't the next. If I ask siri to "lock screen" it tries to find smart home door locks (which i dont have) instead of locking the device screen, eventually I figure out some combination of lock device/screen/phone screen/off etc that works, so siri does know how to do this but isn't smart enough to figure out my intent.

The other issue is that siri unlike google assistant can't maintain a train of thought, You can't say "hey siri dim the bedroom lights" and follow that up with "hey siri..a bit more" unlike with google where it seems to be aware of the context of what it did prior.