Like when watch dealers publish stuff like: https://www.chronext.co.uk/journal/buyers-guide/everything-you-need-to-know-about-the-water-resistance-of-your-watch
30 metres is not the same as 30 metres. If the manufacturer writes that the watch is water resistant to 30 metres, this simply means that the model can withstand the theoretical pressure at this water depth - 3 bar. A bar corresponds to the pressure of one kilogram on a square centimetre large surface, if the force acts vertically on this surface. In practice, however, the pressure in the water varies enormously. As a result of arm movements or jumps, a pressure of more than 3 bar can occur and thus also the risk of water damage. Therefore, a watch that is water resistant to 50 metres should not be worn when swimming.
This video is pretty informative on this topic, skip to around 19:30