OK, first a word of caution
There are some good ones but none are infallible. Some are tainted by user response - so, if the app says 'is this right?' or 'click on the correct identification' it can distort the data when the user is wrong (this is particularly evident in things like moth ID).
So, what does work? 'Seek' is very effective about 80% of the time on many subjects - particularly plants but useless on some others (like moths). Google Lens is also remarkably good about 80% of the time but is one of the tools you have to prepared to totally ignore other times. 'Picture Mushroom' is the best I've found for fungi but always, always, always, confirm by manual ID with good references. Without doubt, the best ID tool I have is Merlin Bird ID which identifies birds from their song. It really is very accurate often identifying birds I had no idea were in the vicinity which I've then been able to confirm with sighting. It does make mistakes (often telling me I have hooded crow because we have carrion crow) but the mistakes are usually obvious. 'Chirp' is a good bird song database if you want to listen to what a particular bird should sound like. 'Pocket Birds' is a good visual reference app.
I have tried and discarded many others
