Whatsapp chat back up / not enough iPhone storage

You will need to delete some data. WhatsApp does not calculate their storage correctly, so you cannot compare what they claim to actual storage space. They are aware of this as seen here:

To ensure that WhatsApp works properly, make sure that your phone has storage space available. You can view how much space WhatsApp takes up on your device and free up storage by deleting items. It's possible that there might be a difference in the storage usage noted by your WhatsApp app and iPhone. This is mainly because of the difference in the way WhatsApp calculates storage vs your iPhone.

https://faq.whatsapp.com/5503646096388294/?cms_platform=iphone&helpref=platform_switcher

For this reason, WhatsApp says your storage space should be 2.05 times what they tell you is currently being used.

You can back up your WhatsApp chat history and media using your iCloud account. Before you get started, check if:

• Your available iCloud account and iPhone storage is at least 2.05 times bigger than the size of your backup.

https://faq.whatsapp.com/481135090640375/?cms_platform=iphone&helpref=platform_switcher