create the file /usr/share/dbus-1/services/org.freedesktop.Notifications.service and add the following
[D-BUS Service]
Name=org.freedesktop.Notifications
Exec=/usr/lib64/xfce4/notifyd/xfce4-notifyd
currently I'm using fedora so the Exec path looks like this, you can look for the executable using find or download the package xfce4-notifyd from pkgs.org, e.g. this is the wanted package in fedora xfce4-notifyd-0.6.3-1.fc36.x86_64.rpm*
go to files and look this executable xfce4-notyfyd then copy its path and put it in Exec in the notifications service. Finally save the service file and restart your session.
* the version may vary :)