Where does the error come from?
As the message suggests, the error comes from a difference in Qt library versions used for building and then running applications.
qt5-styleplugins moved to AUR
In Manjaro, this error started occurring “regularly” following the deprecation of
That package was previously used, among other cases, for applying GTK2 style to Qt applications running in GTK environment (Gnome, Xfce…). Following the drop of GTK2 support upstream, that package became deprecated, and was then moved to AUR.
Qt updates and AUR
Now being demoted to AUR, the package is no longer officially maintained by neither Arch or Manjaro. Consequently, it is no longer rebuilt by the maintainers with every Qt update, contrarily to Qt-based applications still in the repositories. Yet, in order to keep working with other Qt applications, it still needs to be rebuilt so, though now as an AUR package, it is the users’ responsibility to do so.
How to fix it?
There are two simple solutions for that, depending on your use of that package.
If you apply GTK2 style to Qt applications
You need to rebuild it yourself after each Qt update.
pamac build qt5-styleplugins
If you do not have any use for it
You can then simply remove it.
sudo pacman -R qt5-styleplugins
If you don’t have
That package is highlighted here as the most common source of that error. But the logic here applies the very same way for any Qt based package from AUR you may have installed.
If in the exceptional case you find the issue comes from a package from the repositories, you shall then notify the maintainers into updating it: Packaging - Manjaro Linux Forum