I do not why ?

[cfso3515]

I don't know why Couatl for GSX MSFS can't start, this is a log
couatl v5.0 (build 5622)
panic log started on Fri May  2 18:48:28 2025

problem raised by addon __init__.py
Traceback (most recent call last):
  File ".\GSX\assistanceServices\__init__.py", line 4116, in reposition
  File ".\GSX\__init__.py", line 1587, in checkOnGroundState
  File ".\common\criticalsection.py", line 23, in _synchronized
  File ".\GSX\assistanceServices\__init__.py", line 4148, in aircraftEngaged
  File ".\GSX\assistanceServices\__init__.py", line 4273, in materializeTrafficCones
  File ".\GSX\assistanceServices\__init__.py", line 4241, in materializeFuelManHole
  File ".\common\modelCustomization.py", line 1479, in getModelWithTitle
common.modelCustomization.ModelNotAvailable: No model of title FSDT_Fuel_Hydrant_Chevron
{'Airport': 'ZSNJ', 'User Pos': (31.72930277924731, 118.86840277777733, 18.1567 m, 3.15657 m, 327.7999946954305, 0.0017331164809442662, 0.001745329238474369, -6.131225780324897e-06, 3.18211187210083, 1.0)}
and If I load PMDG777-300ER, there will also be an error and the game will exit directly

[virtuali]

common.modelCustomization.ModelNotAvailable: No model of title FSDT_Fuel_Hydrant_Chevron

This error suggest your installation is missing files (not normally possible), because this object is surely part of GSX Pro and it has been since it came out, so it can't be missing because it might have been recently added.

Run an FSDT Live Update CHECK to verify if all files are missing.

and If I load PMDG777-300ER, there will also be an error and the game will exit directly

You should always post the precise, exact, error log, because "an error" is not helping me explaining it. However, if your GSX install is missing such a basic object like the Fuel Hydrant, I'm sure you'll see all sort of errors until you fix it.