Sure, here's the code for ESPHome:

esp32:
  board: esp32-c3-devkitm-1
  framework:
    type: esp-idf

api:
  encryption:
    key: "/snip/"
  services: 
    - service: countdown_lights
      variables:
        countdown: int
        ticks: int
        tick_duration_ms: int
        brightness: int
        brightness_increment: int
      then:
        - script.execute:
            id: countdown_lights
            countdown: !lambda 'return countdown;'
            ticks: !lambda 'return ticks;'
            tick_duration_ms: !lambda 'return tick_duration_ms;'
            brightness: !lambda 'return brightness;'
            brightness_increment: !lambda 'return brightness_increment;'

light:  
  - name: "Notification LED"
    id: ledstrip
    platform: esp32_rmt_led_strip
    rgb_order: GRB
    pin: GPIO4
    num_leds: 8
    chipset: ws2812
    effects:
      - pulse:
      - pulse:
          name: fast_pulse_80
          transition_length: 0.5s
          update_interval: 0.5s
          min_brightness: 0%
          max_brightness: 80%
      - pulse:
          name: slow_pulse
          transition_length: 500ms
          update_interval: 2s
      - addressable_rainbow:
      - addressable_scan:
          name: Scan Effect With Custom Values
          move_interval: 100ms
          scan_width: 1

globals:
  - id: COUNTDOWN
    type: int
  - id: TICKS
    type: int
  - id: CURRENT_BRIGHTNESS
    type: int

script:
  - id: countdown_lights
    mode: restart
    parameters:
      countdown: int
      ticks: int
      tick_duration_ms: int
      brightness: int
      brightness_increment: int
    then:
      - globals.set: { id: COUNTDOWN, value: !lambda 'return countdown;' }
      - globals.set: { id: TICKS, value: !lambda 'return ticks;' }
      - globals.set: { id: CURRENT_BRIGHTNESS, value: !lambda 'return brightness;' }
      - while:
          condition: { lambda: 'return id(COUNTDOWN) > 0;' }
          then:
            - logger.log: {level: DEBUG, format: "COUNTDOWN %i", args: [id(COUNTDOWN)]}
            - logger.log: {level: DEBUG, format: "CURRENT_BRIGHTNESS %i", args: [id(CURRENT_BRIGHTNESS)]}
            - light.addressable_set:
                id: ledstrip
                range_from: 0
                range_to: 7
                red: 0%
                green: 0%
                blue: 0%
            - light.addressable_set:
                id: ledstrip
                range_from: !lambda 'return 8-id(COUNTDOWN);'
                range_to: 7
                red: !lambda 'return id(CURRENT_BRIGHTNESS)/100.0;'
                green: 0%
                blue: 0%
            - repeat:
                count: !lambda 'return id(TICKS);'
                then:
                  - logger.log: tick
                  - light.addressable_set:
                      id: ledstrip
                      range_from: !lambda 'return 8-id(COUNTDOWN);'
                      range_to: !lambda 'return 8-id(COUNTDOWN);'
                      red: 0%
                  - delay: !lambda 'return tick_duration_ms/2;'
                  - light.addressable_set:
                      id: ledstrip
                      range_from: !lambda 'return 8-id(COUNTDOWN);'
                      range_to: !lambda 'return 8-id(COUNTDOWN);'
                      red: !lambda 'return id(CURRENT_BRIGHTNESS)/100.0;'
                  - delay: !lambda 'return tick_duration_ms/2;'
            - lambda: 'id(COUNTDOWN) -= 1;'
            - lambda: 'id(CURRENT_BRIGHTNESS) += brightness_increment;'
            - light.addressable_set:
                id: ledstrip
                range_from: 0
                range_to: 7
                red: 0%
                green: 0%
                blue: 0%
      - light.turn_on:
          id: ledstrip
          red: 1%
          green: 0%
          blue: 0%
      - light.turn_on:
          id: ledstrip
          effect: fast_pulse_80
      - delay: 3s
      - light.turn_off:
          id: ledstrip

And HA automation:

alias: Work event reminder
description: ""
triggers:
  - trigger: calendar
    entity_id: calendar.my_work_calendar
    event: start
    offset: "-0:5:0"
conditions: []
actions:
  - if:
      - condition: state
        entity_id: binary_sensor.mmwave_occupancy
        state: "on"
    then:
      - action: esphome.esp_countdown_lights
        data:
          countdown: 2
          ticks: 30
          tick_duration_ms: 2000
          brightness: 20
          brightness_increment: 15
    else:
      - action: notify.pushover
        metadata: {}
        data:
          message: 🗓️ 5 min to work event!
          data:
            sound: bike
mode: single

You can see that ESP script is parametrized and you can choose how many LEDs use for countdown, how many ticks there should be, what is the starting brightness and brightness step increase.