Insufficient storage for WhatsApp backup and photo synchronization on iPhone

Hello everyone, I am running into some memory issues with my iPhone. My storage is almost completely full (I have one gigabyte remaining, out of a 64 GB total) and I am trying to perform a backup using the data transfer option to an iPhone (which in this case will be restored back onto the one I am currently using) via the temporary and free iCloud extension, in order to clear a large part of the "System Data".

Watching a video, I saw that to avoid losing WhatsApp messages, I should first back up the chats using my own iCloud storage (I currently have the 50 GB plan), which is also full. I proceeded to clear some gigabytes of space by removing a few photos to perform the backup, but despite this, it still requires free local space.

I then thought of uploading the photos that are currently saved locally on my device (because synchronization has been interrupted for a while), but I can't do that because it says synchronization is interrupted, again due to insufficient local space.

I am stuck in this loop and don't know what to do. If you could provide me with a solution, I would be grateful.

[Re-Titled by Moderator]

Original Title: Storage issue