SegWit fixed transaction malleability by just moving the signature out of the block of data that’s being hashed to form the transaction id.
However, Schnorr does not suffer from signature malleability (https://medium.com/digitalassetresearch/schnorr-signatures-the-inevitability-of-privacy-in-bitcoin-b2f45a1f7287):
Non-malleability: ECDSA signatures are inherently malleable, which may
enable a third party without access to the private key to alter an
existing valid signature and double-spend funds. This issue was
formally discussed in BIP62. In comparison, Schnorr signatures are
Consequently, is a Schnorr signature still segregated from the data that’s being hashed, and if yes, why?