GoPro Hero 7 Silver uses a smaller 10MP sensor and while you do get 4K video, it is only limited to 30fps while slo-mo is restricted to 60fps. The Silver gets the same waterproof protection as the Black i.e. up to 33 feet or 10 meters, as well as touch screen and voice control functionality.
Hero 7 Silver, however, misses out on features such as live streaming to social media, and HyperSmooth video that produces Gimbal-like effects. You, however, do get the GPS as the higher variant.