It seems like one is showing GiB and the other GB, which are two different units.
KB = 1000B KiB = 1024B
Which doesn't seem significant but it adds up.
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
It seems like one is showing GiB and the other GB, which are two different units.
KB = 1000B KiB = 1024B
Which doesn't seem significant but it adds up.
I'd like to add that GB is pronounced Gigabyte, and GiB is pronounced Gibibyte. For the full list of units you can check this
It’s not this significant (3x). it should be closer to 7%. My guess is that OP is using something like btrfs, whose data used is calculated differently due to the CoW nature, and btop++ is using using a generic tool to estimate disk usage rather than the btrfs utility that DUA is almost certainly using.