I have been suggested by someone with YAML knowledge to use anchors, but I don't know if these are supported, trying anyway

esphome/device_packages/sensor-box-diy.yaml

@@ -8,16 +8,14 @@ light:
     num_leds: 5
     type : GRB
     name: "${friendly_devicename} PM25"
-    effects: !include
-      - file: ../partials/effects.yaml
+    effects: *shared_effects
   - platform: neopixelbus
     variant: WS2812
     pin: D3
     num_leds: 5
     type : GRB
     name: "${friendly_devicename} PM10"
-    effects: !include
-      - file: ../partials/effects.yaml
+    effects: *shared_effects
   - platform: binary
     name: "${friendly_devicename} Lamp"
     output: relay

esphome/partials/effects.yaml

@@ -1,13 +1,14 @@
-- strobe:
-- flicker:
-- addressable_rainbow:
-- addressable_color_wipe:
-- addressable_scan:
-- addressable_twinkle:
-- addressable_random_twinkle:
-- addressable_fireworks:
-- addressable_flicker:
-- addressable_color_wipe:
+light: &shared_effects
+  - strobe:
+  - flicker:
+  - addressable_rainbow:
+  - addressable_color_wipe:
+  - addressable_scan:
+  - addressable_twinkle:
+  - addressable_random_twinkle:
+  - addressable_fireworks:
+  - addressable_flicker:
+  - addressable_color_wipe:
         name: Kingsday
         colors:
           - red: 78%
@@ -28,11 +29,11 @@
             num_leds: 6
         add_led_interval: 100ms
         reverse: true
-- random:
+  - random:
       name: "My Slow Random Effect"
       transition_length: 30s
       update_interval: 30s
-- random:
+  - random:
       name: "My Fast Random Effect"
       transition_length: 4s
       update_interval: 5s