Characteristic of Public Key? Is Public key used directly to encrypt a message or it is used to derive other keys ?
Can we decrypt a message with same public key using which it was encrypted ?

So far I understand, as PKI is based on mathematical functions which are hard to solve in opposite direction, an encrypted message should not be decrypted using same Public key, but article https://blog.cloudflare.com/encrypted-sni/  mentiones that Public key is used to derive some other keys which are actually used for encryption, thus need clarification.
Is Public key used directly to encrypt a message or it is used to derive other keys?


A public key is used to encrypt a message.

Example:

If Alice wants to send a message to Bob she would take Bob's public key and encrypt the message and send the encrypted message to Bob.

A key to derive other keys is done with a Key derivation function and this key is commonly called a "master key", so it has nothing to do with public-private-key-encryption.




  Can we decrypt a message with same public key using which it was encrypted?


No, you can only decrypt the encrypted message with it's corresponding private key (you always create a private &amp; public key pair together).