After update qt base, got apps, e.g. qpdfview, utilizing it stumble at
Cannot mix incompatible Qt library (5.15.3) with this library (5.15.4)
Any decent knowledge on what actually is going on and its solution?
what did you install from the aur that is qt based?
guess, one of this below must be updated to in accordance with qt base
$ pacman -S qt5-imageformats qt5-multimedia qt5-speech qt5-svg qt5-tools qt5-wayland qt5-x11extras
to solving but not surely know which one precisely
All of those have been built against 5.15.4 and should be that version.
Make sure you update qt5-styleplugins to 5.0.0.20170311-29.1 (from [galaxy]).