Seawater salinity does not have a correlation to tides. Just because seawater has a higher salinity than lake water, it does not mean salinity causes tide.
Some flat-Earthers claim tides are the result of salinity. They are wrong. There are bodies of water that do not have tides as large as seawater, but their salinity is much higher than seawater.
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 are the result of salinity. This corresponds to the very simple observation that seawater has tides, but other bodies of water do not.
However, with more careful observation, it is not true. Not every lake has a low salinity. Some lakes even have a much higher salinity than seawater. The Garabogazköl lagoon, for example; has the salinity 10× the seawater average, but it 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.
And thus, their assumption that tides are the result of water salinity is disproven very easily.