Google isn’t the best place to collect height maps from, just wanted to show you how different yours looks than the others. The ones you find on google are mostly 8bit and include artifacts.
Here is one I made right now for you to test with.
And here is the settings for it. (Default settings, and in order to get the proper settings (if you have changed them and can’t go back) close the engine, launch again and then try to import the height map again)
Download this software and create your own height maps. (Basic edition is free)
Edit: You can also use .png so don’t resave as .raw the one I uploaded for you.