Per BIP-341, if you want to create a Taproot output that is only spendable via the script-path spend (and not a key-path spend), you must "pick as internal key a point with unknown discrete logarithm."

This requires using a nothing-up-my-sleeve (NUMS) point as your internal public key which has no valid corresponding private key.

How should I go about choosing such a point? Are there canonical examples to draw from?