It appears you are misundertanding what a <form> is used for.
A form is used to collect user inputed data and then send it to a server side script for processing after the submit button was clicked by the user.
If you want to open the select menu in a new window, I would put the <div> containing the <select> in a separate html file and then use window.open() in the first html file to open the second html file containing your menu.
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