Hey there @RoyalKirin !
Yesterday I’ve come up with this same issue and din’t know at all how to get rid of that seam.
Today I discovered (sincerely don’t know why, but it seems to be working) that selecting ‘WaterBodyOcean’ and scrolling down to ‘Wave’, go on ‘Waves Source’.
Right there I got ‘Water Waves Asset Reference’ or something similar selected. If you click on the dropdown and switch to another option, then back to ‘Water Waves…etc’ you’ll notice that the seam disappears and the water level on your landscape is now the same as the rest of the ocean.
Hope this works for you!