The "for fun" part is really important here. Addictive behavior comes from a hijacked dopamine system, into which you slowly get lured in. This makes it applicable to social media, drugs and if you squint, even to broad obsessions.

This doesnt help the gambling distinction though. What activities can take over your neurological reward mechanism? Pretty much everything, like neurotically washing your hands. So you have to factor in societal scale and amount of (potential) harm and this is where the vague debate begins. A key point is a dealer/platform, profiting from your behavior, to exclude neurotics.

A striking observation i made was, that gambling machines have deliberate delays between action (eg pull the lever) and reaction/reward for the brain to create tension and to break it with a dopamine spike. This deliberate design is how the machine exploits your brain and makes you an addict. A similar system is the endless social media feed (or even worse brainrot short videos). You scroll, you see new stuff, you identify content maybe emotionally. Its the same fast stimulus-reward cycle. Meassured in 1-2 seconds, same as gambling machines.