A Stone Golem has the ability to create a slow effect on nearby creatures:
Slow (Recharge 5-6): The golem Targets one or more creatures it can see within 10 ft. of it. Each target must make a DC 17 Wisdom saving throw against this magic. On a failed save, a target can’t use reactions, its speed is halved, and it can’t make more than one Attack on its turn. In addition, the target can take either an action or a Bonus Action on its turn, not both. These Effects last for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
This is similar to, but not the same as the results of the slow spell.
Can you use dispel magic to remove this effect? It isn’t technically a spell even though it is magical.