Folder Formats: Quick Guide explains how to always have the same display mode in all folders.
You can have that drop-down back, but if you use it it will turn content type formats back on, which will (depending on other settings) put you back to having the display mode automatically switch to thumbnails, which is not what you want.
Instead, it might be better to create buttons or a menu which switch to specific folder formats, or which change the display mode, or whatever you want. We can help you set that up, if you tell us what you want in it. (If you just want a quick way to switch in and out of thumbnails mode, that's already there on the default toolbar.)