[SEC][1] encoded public keys are either:
* **Uncompressed** 65-byte encoding: 0x04 + [32-byte X coordinate] + [32-byte Y coordinate]
* **Compressed** 33-byte encoding:
  * 0x02 + [32-byte X coordinate] (if Y coordinate is even)
  * 0x03 + [32-byte X coordinate] (if Y coordinate is odd).

P2TR output don't use SEC encoded public keys at all, but raw "x-only" public keys, in which only the 32-byte X coordinate itself is revealed. The used [BIP340][2] signature scheme is constructed in such a way that the Y coordinate does not matter.


  [1]: https://www.secg.org/sec1-v2.pdf
  [2]: https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki