Missing runtime dependencies can make steamclient64.dll fail to load.

Start with those. If they don’t work, methodically work through the advanced fixes. Do not panic, and absolutely do not download DLLs from the internet.

When you search for this error, you may see websites offering a free download of the steamclient64.dll file.

Click "Steam" in the top-left corner of the app and select "Check for Steam Client Updates."

or "Failed to load steamclient64.dll"