It's a neologism for multimedia content that produces some kind of addiction, such as social media catching its users, who feel they can't stop checking them. A more specific case is the providers of videos, images or news, which are specially designed to capture attention and that users do not leave their platforms. It is formed by the prefix info- (for "information") and dopamine, a neurotransmitter hormone that is popularly more associated with sensations in the reward state, the pleasure you feel when getting something.
INFODOPAMIN Dopamine is a natural and also laboratory neurotransmitter substance that neurons use to intercommunicado. Dopamine is often considered to be the cause of pleasurable sensations and relaxation. The info prefix is redundant and reinforces the fact that dopamine transmits information from neuron to neuron.