user136800: I can't seem to find any cli commands for this. Is it even possible? Or does RBF need to be opted into on a per transaction basis?
I would just like every transaction sent by my node to be RBF enabled.

user5406: You're looking for walletrbf=1.
You can configure bitcoind to always create transactions that signal replaceability by using the -walletrbf startup option or setting walletrbf=1 in the config.
Relatedly, Bitcoin Core creates by default replaceable transactions from the GUI since v0.16.0, and will also create replaceable transactions by default when using RPCs starting with the upcoming v24.0 release (see PR 25610).
Orthogonal to your question, some people contend that all transactions should always be replaceable even if the sender did not opt-in by signaling replaceability originally. Also to be released in v24.0, PR 25353 added the -mempoolfullrbf startup option which would configure a node to permit transactions in its mempool to be replaced per the established replacement rules without requiring the original transaction to have signaled replaceability. If sufficient node operators and miners choose to adopt to this updated mempool policy, the possibility of doing replacement without prior signaling may emerge on the network.

136800: <p>I can't seem to find any cli commands for this. Is it even possible? Or does RBF need to be opted into on a per transaction basis?
I would just like every transaction sent by my node to be RBF enabled.</p>
 5406: <p><strong>You're looking for <code>walletrbf=1</code>.</strong></p>
<p>You can configure <code>bitcoind</code> to always create transactions that signal replaceability by using the <code>-walletrbf</code> startup option or setting <code>walletrbf=1</code> in the config.</p>
<p>Relatedly, Bitcoin Core creates by default replaceable transactions from the GUI since v0.16.0, and will also create replaceable transactions by default when using RPCs starting with the upcoming v24.0 release (see <a href="https://github.com/bitcoin/bitcoin/pull/25610" rel="nofollow noreferrer">PR 25610</a>).</p>
<p>Orthogonal to your question, some people contend that all transactions should always be replaceable even if the sender did not opt-in by signaling replaceability originally. Also to be released in v24.0, <a href="https://github.com/bitcoin/bitcoin/pull/25353" rel="nofollow noreferrer">PR 25353</a> added the <code>-mempoolfullrbf</code> startup option which would configure a node to permit transactions in its mempool to be replaced per the established replacement rules without requiring the original transaction to have signaled replaceability. If sufficient node operators and miners choose to adopt to this updated mempool policy, the possibility of doing replacement without prior signaling may emerge on the network.</p>
