How to stop Visual Studio from opening a file on single click?

This is called the Preview Tab feature. To change that behavior, go to:

Tools -> Options -> Environment -> Tabs and Windows

Then look for the "Preview Tab" section, and uncheck the options therein:

Options Window > Environment option > Tabs and Windows sub-option > Preview Tab section

Option 1: Using icon in Solution Explorer

You can enable or disable the feature in Solution Explorer using the "Preview Selected Items" button.

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The icon is a Tab aligned to the right.

You can enable or disable the feature by going into Tools > Options and then Environment > Tabs and Windows.

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