is there any way to delete all the data in Memgraph and reset the next internal ID to be created to zero?
I've noticed that every node that is created gets the automatically new ID. When I delete the node that ID is not used again but a new one is used.
Yes, you are right this is intentional. The only way in which you can get same ID again is by deleting your data directory or creating a new Memgraph instance. This is because internal ID(GID) shouldn't be used by users, if they need some way of manipulation, they should use properties for that.