What is Janna's most reliable build when she mainly has to deny the enemy's best timing?

Utility build focused on protecting carries.

When should you truly adapt Janna's build instead of pushing the standard utility-support route?

You should adapt as soon as the enemy draft stops you from playing the timing the build was meant to serve. If you need to survive longer, absorb more poke, or answer a specific engage pattern, the purchase order must move before you even think about the final six-slot build.

Which enchant should Janna choose when the real issue is holding the first shock and then resetting tempo?

Redemption often remains the most reliable choice when Janna mainly needs to extend the fight after breaking the entry. If your team needs extra time to play again, this enchant gives more value than a more aggressive choice.

Janna Wild Rift Best Build Guide (Patch 7.2a)

Janna Wild Rift Best Build Guide

Anti-engage and defensive-tempo build: Janna wins when she denies the enemy the right to cleanly open the sequence they wanted to play. The build must therefore reinforce her response frequency, the quality of her peel, and enough safety to replay several denials in the same fight.