I think 'thread_count' has been deprecated in the latest release of the CatBoost. You need to use two parameters, 'devices' and 'task_type', to specify multiple CPUs or GPUs.
The possible values for the parameter 'task_type' are 'CPU' and 'GPU'.
For the parameter 'devices', you can specify the unit ID, multiple unit IDs, or a range of unit IDs. E.g. 'devices'='1' (single unit), 'devices'='0:4:5' (multiple units), 'devices'='0-16' (range of units).
Here are some examples:
For CPU:
from catboost import CatBoostClassifier
model = CatBoostClassifier(iterations=500, task_type='CPU', devices='0-4') # to use 0 to 4 CPUs
For GPU:
model = CatBoostClassifier(iterations=500, task_type='GPU', devices='0-4') # to use 0 to 4 GPUs