Unable to Backup on iCloud or with PC

iOS 18.3

iPhone 14

Whatsapp 157GB total. 7,3GB with no media

iCloud 19/50GB

When I try to backup, a warning appears about how the backup doesn't include an app at random. At the end of this message two options appear:

1) Cloud settings: if I select this an option, momentarily the apps list appears and then goes back to the Backup screen.

2) Continue: The backup starts but it stops during the calculation space phase. It says that is impossible to backup the phone because there's not enough space.

I also tried to backup with iTunes and with iCloud but the operation was also stopped midway.

Another weird thing is that the backup of Whatsapp is stuck in the message: You have not logged in with your iCloud account so is not possible to make a backup.

What can I do?