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

@@ -1,3 +1,4 @@
+light: &shared_effects
   - strobe:
   - flicker:
   - addressable_rainbow: