Oh my gosh I’m so sorry. There’s been a misunderstanding and I didn’t realize it until you quoted me. You mean the SharedAssets FOLDER. I thought you were meaning assets that were used by more than one thing, in general!
You are fine. Your SharedAssets is something used by UE5 to do yes, exactly what you were saying. Here’s the thing. Everything in UE is given a (hidden) ID#, and ALL things have a 100% unique one per project, including duplicated things! This is something that determines how the sharedAssets act. There’s only one SharedAssets folder, you’re good 
You can modify your multiple landscapes separately and it will in no way affect the others, as long as they are duplicates and not children, which you’d know if they were.