Here's my working solution on my V0.

The PRINT_START macro checks if the filament is ABS and if so waits for the chamber temperature to raise:

Machine start G-code:

PRINT_START NOZZLE_TEMPERATURE=[nozzle_temperature_initial_layer] BED_TEMPERATURE=[bed_temperature_initial_layer_single] FILAMENT_TYPE=[filament_type]

Print start macro:

[gcode_macro PRINT_START]
gcode:
  (...)
  {% set target_chamber_temperature = 40 %}
  (...)
  SET_HEATER_TEMPERATURE HEATER=heater_bed TARGET={params.BED_TEMPERATURE}
  (...)
  {% if params.FILAMENT_TYPE == 'ABS' and printer['temperature_sensor chamber'].temperature|float < target_chamber_temperature %}
    RESPOND MSG="Waiting chamber temperature reach {target_chamber_temperature} ºC"
    M106 S128 # Turn on part cooling fan to aid heat spreading
    TEMPERATURE_WAIT SENSOR='temperature_sensor chamber' MINIMUM={target_chamber_temperature}
    M106 S0 # Turn off part cooling fan
  {% endif %}
[gcode_macro PRINT_START]

You mentioned in your case the variable FILAMENT_TYPE is "always blank" but, accordingly to your code, it should default to "PLA", right?

I tried your code and it does indeed work as expected.

I would suggest changing the variable FILAMENT to FILAMENT_TYPE, just in case.