Cycles has a Shadow Catcher node. Unfortunately, it doesn't work in Eevee. There is a way to create it with nodes though, but it's not simple. Luckily, there are some material setups for good shadow catchers out there.

Full disclosure, I did not create this screen cap. It was posted publicly somewhere, but I can't recall exactly where. I think I found it on Pinterest a while back. It works though.

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