DerGroBe
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I had a similar problem. To solve it, just place a piece of land under the bridge, but in such a way that the bridge is not completely on it, but only partially (this is hard to describe in words). The land block should be inside the texture of the bridge support, but not directly under it, otherwise the bridge will simply rest on this land block.
What if, for example, you first place the bridge foundation and then create a plateau underneath it? There remains a small space, a void. As I understand it, it doesn't need to be filled, or is it still desirable to create a hill?