The digital channels at your disposal to publish your video on are numerous to say the least. However, they also tend to work very different from each other. Targeted towards different groups, the various sites have varying audiences that might be very different from each other, especially in how they consume content on the platforms. A YouTube user, for example, may happily watch a video that goes on for 8 minutes, while an Instagram user will probably not give it more than 15 seconds. TikTok for example is heavily popular with the younger generation, where videos hardly go any longer than 30 seconds.
Social media sites tend to stir their algorithms into the direction that gets the most engagement from users. Thus, if short videos are heavily favored on a site, the algorithm will likely push short videos because the developers know that this keeps people engaged. So when assessing the perfect video length for different channels, make sure to find out and consider what length tends to do best on the platform.