Run the handler after the interface configuration.

handlers/main.yml

@@ -1,4 +1,4 @@
 ---
 - name: Netplan Apply
   ansible.builtin.command:
-    cmd: netplan Apply
+    cmd: netplan apply

tasks/network-interfaces.yml

@@ -31,3 +31,9 @@
         mode: "0644"
       when: net_ints is defined and net_ints | length != 0
       notify: Netplan Apply
+
+- meta: flush_handlers
+  tags:
+    - network_interface
+    - networking
+