user123331: 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
provably non-malleable.

Consequently, is a Schnorr signature still segregated from the data that's being hashed, and if yes, why?

user101498: Schnorr (bip-340) signatures have been introduced as part of v1 Segwit outputs with the CHECKSIGADD opcode. Therefore bip-340 signatures are part of the witness and are not part of the hash forming the txid.
Script malleability is only a single among a lot of benefits brought by Segwit, and we shouldn't drop all the others (and encourage using legacy transactions) because part of the proposal does not need one of them.
For example, one of these benefits is simpler Script versioning and rolling out the CHECKSIGADD behaviour using the legacy versioning (NOP ops) would be a bit "dirty" (in addition to adding the incentive to use legacy transactions that are more expensive for the network to process).

123331: <p>SegWit fixed transaction malleability by just moving the signature out of the block of data that's being hashed to form the transaction id.</p>
<p>However, Schnorr does not suffer from signature malleability (<a href="https://medium.com/digitalassetresearch/schnorr-signatures-the-inevitability-of-privacy-in-bitcoin-b2f45a1f7287" rel="noreferrer">https://medium.com/digitalassetresearch/schnorr-signatures-the-inevitability-of-privacy-in-bitcoin-b2f45a1f7287</a>):</p>
<blockquote>
<p>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
provably non-malleable.</p>
</blockquote>
<p>Consequently, is a Schnorr signature still segregated from the data that's being hashed, and if yes, why?</p>
 101498: <p>Schnorr (bip-340) signatures have been introduced as part of v1 Segwit outputs with the <code>CHECKSIGADD</code> opcode. Therefore bip-340 signatures are part of the witness and are not part of the hash forming the <code>txid</code>.</p>
<p>Script malleability is only <a href="https://bitcoincore.org/en/2016/01/26/segwit-benefits/" rel="nofollow noreferrer">a single among a lot of benefits brought by Segwit</a>, and we shouldn't drop all the others (and encourage using legacy transactions) because part of the proposal does not need one of them.</p>
<p>For example, one of these benefits is simpler Script versioning and rolling out the <code>CHECKSIGADD</code> behaviour using the legacy versioning (<code>NOP</code> ops) would be a bit &quot;dirty&quot; (in addition to adding the incentive to use legacy transactions that are more expensive for the network to process).</p>
