Be weary as the docs on Tiled landscape probably have a wrong size on them.
The sizes that work best seem to be those that epic reccomends.
I never did understand the extra pixel thing, but it’s pretty easy to circumvent.
create a landscape of the recommended size you are interest in. export/save the heightmap. Take its pixel size. Use it to split your bigger map into squares of that size.
Using tiles of the exact recommended size everything seems to work ok.