Twitch's official Twitch Charity integration currently creates a Donate button that replaces the Subscribe button; however, viewers can still choose to Subscribe during these charity streams, and there's no mechanism for Bits to be used to donate.

Twitch Charity is explicitly marketed as a way to avoid having to count Subs/Bits as part of the donation process, and yet Twitch Charity does not change this issue whatsoever. Streamers would still have to manually calculate their income from a charity stream and donate that amount (potentially having to wait for their next payout to be able to do so, in some cases), or they have to accept that they'll be profiting off of a charity stream.

Additionally, the streamer then has to constantly remind chat not to Sub or donate Bits, and/or some viewers will be blindsided if they find out that even at best, 50% of their Subscription payment cannot be donated to the charity (since Amazon will still take its cut of Subs). If Twitch wanted to go above and beyond these basic requirements, it could even enable Prime Subs as eligible Donations - this is unlikely to happen, but pie in the sky!