Generally speaking, the ‘Soap Opera Effect’ is most often associated with frame interpolation just as Elusein outlines above. But the same phenomena occurs with any frame rate that exceeds 24/25 fps. The term literally finds its roots in soap operas made for television (NTSC 29.97 fps). It gets more prominent at 48 and 60fps, while becoming intolerable at 120 and 240 fps. There’s just something about fast frame rates that shutdown our natural ability to blur rapid motion. To suddenly observe that motion without natural blurring is jarring to the senses. At least with facial close-ups.
Beyond those close-ups, the appeal of 24/25 fps gets much more subjective. The proponents of 24/25 fps see no limits to the appeal in cinematography, even if it means judder in high motion scenes. I presume that’s because their brain literally ignores the judder as the motion blur causes disengagement with scene details. Or they simply accept the judder as a temporary inconvenience that’s subordinate to the greater benefits of low frame rates.
To everyone outside of the financial influence of Hollywood, and particularly with a brain tuned for processing motion details (such as gamers), the judder and artificial blurring associated with low frame rate cinematography simply becomes nauseating. I personally believe that 30 fps (29.97 fps for maximum compatibility among camera output) provides the best experience among tradeoffs in cinematography (specifically focusing on landscape drone footage). We can generally get away with up to 7.5º /sec at 30 fps (depending on lens focal length and field-of-view) while avoiding noticeable judder. Others will certainly prefer 60 fps to avoid all judder with cinematic movement to include parallax-induced judder in orbit shots (rapidly spinning background relative to a near-motionless POI in the foreground). Sports unquestionably demand 60 fps as the movement is incompatible with- and unrelated to- cinematic goals.