Could not backup the iPhone xxx because an error occurred while reading from or writing to the iPhone
I'm trying to backup an iPhone 11 Pro (IOS 14.3) to my MacBook (macOS 10.15.7 Catalina), the two devices are connected by USB cable. But I keep getting this message "Could not backup the iPhone xxx because an error occurred while reading from or writing to the iPhone."
The USB cable and MacBook are fine, I can backup the other iPhone 11 Pro we have. It's just this one iPhone that's giving problems. I also have 260 GB of free storage on my MacBook, the problem iPhone has 64 GB which is half used.
Does anyone have any idea how I can fix this? Please don't say "in iTunes..." because macOS Catalina does not have iTunes, Finder is used instead.
Many thanks.
iPhone 11 Pro