What is the lock indicator on Karabiner-Elements and Karabiner-EventViewer icon
A lock indicator is shown on Karabiner-Elements and Karabiner-EventViewer icon since macOS 11.0 (Big Sur).
These indicators show that these files are protected so that they cannot be deleted from Finder.
Why these files are protected
This protection is intended to prevent incomplete uninstallation.
Karabiner-Elements is a system-wide software, and files are installed in appropriate locations besides the Applications folder.
Therefore, if you just put the application icon in Trash like a normal app uninstallation, some files will be left behind.
The file protection forces to use the built-in uninstaller and remove installed files properly at the uninstallation.
Advanced topic
This file locking is achieved with schg and uchg flags.
You can unlock these files by the following commands in Terminal.
sudo chflags nouchg,noschg /Applications/Karabiner-Elements.app
sudo chflags nouchg,noschg /Applications/Karabiner-EventViewer.app
(Administrator password is required to run the above command.)