No correlation exists between salinity and tide. These bodies of water have higher salinity than the seawater average, yet they have no tides or smaller tides than the ocean.
Tides occur on the ocean with salt water, but seemingly not on lakes with fresh water. Flat-Earthers use it to “prove” salinity causes tides. In reality, there are bodies of water with a higher salinity than the ocean but smaller tides.
Flat-Earthers began with the assumption that gravity does not exist. But they need something to “explain” the phenomenon of tides. So, they invented an ad-hoc hypothesis that tides result from salinity. The “explanation” seemingly corresponds to the casual observation that seawater has tides, but rivers and lakes do not.
But with more careful observation, we can find lakes having a much higher salinity than the ocean. The Garabogazköl lagoon, for example, has a salinity ten times the seawater average but has no tides.
The same thing also applies to the world ocean. The global ocean does not have the same amount of tides everywhere. Some have above average tide; others have lower than the average. Having a higher salinity does not mean having higher tides and vice versa. The Mediterranean sea, for example, has a higher salinity than the world average but has far less tide.