https://bugs.kde.org/show_bug.cgi?id=371455
--- Comment #46 from Aaron Goldblatt ---
This issue is still present in Ubuntu 20.10 (pre-release, I know):
Operating System: Kubuntu 20.10
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.14.2
Kernel Version: 5.8.0-19-generic
https://bugs.kde.org/show_bug.cgi?id=426879
Bug ID: 426879
Summary: Very Large Wallpaper Directories Hang plasmashell
Product: plasmashell
Version: 5.18.5
Platform: Ubuntu Packages
OS: Linux
Status: REPORTED