I am sorry because my question is off-topic, but I don’t want to create a new topic

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why Bitcoin Core 0.16.0 developers start using/enabling native segwit addresses by default while sign message/verify message doesn’t support segwit addresses? I know this is because some RPCs do not yet support segwit addresses but why they make it default? "it’s better to make a new private key and full support segwit by default, correct?"
Sources : https://bitcoin.org/en/release/v0.16.0

It is neither a bug nor an abandoned feature. It is just that we are still working on creating a more generalized signing scheme that lets people sign with things like P2SH addresses (e.g. sign with a multisig address). There is simply no standard yet for signing with such scripts or with Segwit.

Note that you don't actually sign with an address. You sign with a public-private keypair and your wallet interprets it as an address. Your wallet could just as easily interpret it as a segwit address. We are working on creating something that actually specifies the address type, and more generally, allows signing with scripts.