when i was testing my android signer, i found that amethyst usually ask the signer to decrypt the private zaps. but these private zaps aren't send to me or send by me.
i don't know how to stop it. 

 Yes, the only way to see if the private zap is to you or for you is if the signer is able to decrypt it.
In amber there's a way to reject a event for ever.

https://github.com/nostr-protocol/nips/blob/master/55.md#L291

https://github.com/greenart7c3/Amber/blob/master/app%2Fsrc%2Fmain%2Fjava%2Fcom%2Fgreenart7c3%2Fnostrsigner%2FSignerProvider.kt#L272