Here are the steps for setting up KeePassXC integration with LibreWolf on Linux:
Install LibreWolf, KeePassXC, and the KeePassXC browser extension in LibreWolf.
Enable Firefox browser integration in the KeePassXC settings.
Symlink Firefox's native-messaging-hosts directory into LibreWolf's configuration directory:
ln -s $HOME/.mozilla/native-messaging-hosts $HOME/.librewolf/native-messaging-hosts
In LibreWolf, navigate to about:config in the URL bar, and set the property widget.use-xdg-desktop-portal.native-messaging to have a value of 1.
If using the Flatpak version of LibreWolf, then give LibreWolf access to the symlinked native-messaging-hosts directory using a tool like Flatseal:
Restart both KeePassXC and LibreWolf. When LibreWolf reopens, it may ask you to confirm that you want to enable native messaging (though I don't recall the exact wording); and you should confirm it.
Finish setting up the KeePassXC browser extension in the usual way!