TestTMProMaterialChanger

public class TestTMProMaterial : MonoBehaviour
{
    [SerializeField] private TMP_Text _tmpText;
    [SerializeField] private Material[] _materials;

    private int _index = 0;

    private void Awake() => _index = 0;

    private void Update()
    {
        if (Input.GetKeyUp(KeyCode.Space))
        {
            var index = _index < _materials.Length - 1 ? _index++ : _index = 0;
            var material = _materials[index];
            _tmpText.fontMaterial = material;
        }
    }
}