Whatsapp backup to icloud stuck on Preparing

Hello angel.yasin381,

Welcome to Apple Support Communities!

We want to make sure all yours apps are working as expected.

For this sort of issue with a third-party app, you'll want to contact the developer:

"When to contact an app developer for help

• If an app isn't working, but the issue doesn't affect other apps
• If you can't use an in-app purchase, such as a bonus game level or "remove ads" 

Contact the developer of an iOS, iPadOS, or watchOS app

1. Open the App Store on your iPhone or iPad.
2. Search for the app, then tap it. If you can't find it, tap the account button  or your photo at the top of the screen, tap Purchased, tap "Not on this [device]," then tap the app.
3. The app's product page appears. Scroll to the Ratings & Reviews section, then tap App Support. If you don't see App Support, make sure that you're signed in with the correct Apple ID."

This Apple Support page has the full details: How to contact an app developer - Apple Support

We hope these steps can help isolate and resolve the issue so you can create your WhatsApp backup.

Cheers!