Hello. What is the optimal number of slots that should be configured in the Flink task manager? is it related to the CPU core in the node?

yes it is related more to memory, memory will be divided between slots, so you need to configure as per job pattern(IO intensive or cpu intensive)

Thanks, but I have a mixed workload in the cluster. Does the memory is divided equally, what if I have 4 GB and 4 slots in a node? One slot is 1 GB and if other slots are not used does the memory of other slots are shared to slot 1?

almost, please exclude some reserved network and flink memory