If you take a look at the examples and the documentation I shared you will see that you have to instantiate your model in the same strategy scope than the trainer will use with. For example in the run_tf_glue.tf file:
with training_args.strategy.scope():
        model = TFAutoModelForSequenceClassification.from_pretrained(
            model_args.model_name_or_path,
            from_pt=bool(".bin" in model_args.model_name_or_path),
            config=config,
            cache_dir=model_args.cache_dir,
        )

If you don’t do that you cannot use the TFTrainer for any model not only Longformer.
It’s a small world indeed