There is nothing in John chapter 6 to indicate that Jesus was speaking in parables. Especially since He let some of the disciples leave. He could have called them back and told them that He was speaking in parables, but He didn’t. “Many therefore of his disciples, when they had heard this, said, This is an hard saying; who can hear it? From that time many of his disciples went back, and walked no more with him.” John 6:60, 66
Jesus already knew they were going to leave, even before he got into his parable...Nothing he could have said would have stopped them...