How do I delete my Twitch account for good, and does it wipe my follows and clips?

Twitch deletion is on their website, not the app. Go to twitch.tv, log in, and visit the account deletion page (twitch.tv/user/delete-account, or Settings > the disable/delete option). Confirm with your password. Your channel, clips, follows and VODs are removed. There's about a 14-day window where the account is deactivated and you can reactivate by logging back in, but after that it's permanent. Cancel any Turbo or subscription first so you're not billed. If you were a partner or affiliate, contact support, there can be extra steps.

The 14-day reactivation window is handy if you're unsure, log back in within two weeks and it's restored. After that, gone for good.

Cancel any Twitch Turbo or Prime sub before deleting, otherwise the billing can carry on. Same trap as most apps.