The taskbar looks like:
I find that only svg icons disappear, meanwhile png icons is good.
Switching theme make no difference.
So, check journal, there’s some error message like:
12月 25 10:53:58 debian plasmashell[2247]: qt.svg.draw: The requested buffer size is too big, ignoring
I thought this is bug of qt-svg and found QTBUG-123010.
But the above issue had been fixed in qt6-svg 6.7.0, and the version in my system is 6.7.2.
Then, I found the same issue another one reported in manjaro forum.
The commands in that thread make no luck:
rm ~/.cache/icon-cache.kcache && kbuildsycoca5 --noincremental && kbuildsycoca6 --noincremental
Finally I found some old packages in my system and remove them:
apt remove kup-backup desktop-base libkf5config-bin
apt autoremove
All svg icons come back after rebooting system.
I cann’t sign up manjaro forum successfully, so record my method here.