I keep my Documents, Downloads, Music, Pictures and Videos in a separate partition which are symlinked to my Home folder.
However, this means Dolphin cannot perform search in the root of these symlinked directories, although there's no such problem in any subdirectory, that is, unless it's also a symlinked directory.
KFind does not have this problem.
I wonder if there's a workaround for this.

This is related to: https://bugs.kde.org/show_bug.cgi?id=333678
Until it is resolved, this might be a good workaround:
1. Stop file search indexing with this command: balooctl disable
2. Use bind-mounts instead of symlinks by removing existing symlinks and adding your symlinked directories to /etc/fstab like this: /source/ /destination/ none defaults,bind 0 0
3. Delete existing file search database with this command: rm -r ~/.local/share/baloo
4. Add (or modify) this entry to ~/.config/baloofilerc configuration file's General section: first run=true
5. Restart the computer
6. Check if baloo is running with this command: balooctl status
7. If not, use this command to enable it: balooctl enable