Ah yes, you’ve stumbled across the one element Microthemer can’t directly target with double-click: the select element. For now, the only way to move Microthemer onto select elements is to double-click the element that contains the select element, then go to the Inspector tab of the selector wizard, and click the down arrow one or more times.
In a new update, due in February, there will be an alternative way to target elements with single click, an event select elements respond to.
I hope that helps. Please let me know if you require further guidance.