Maintenance mode (or "Under Construction") is the state that a website is put in, if the website content shall remain hidden from website visitors temporarily. Usually, maintenance mode is being used if the website is about to receive a major overhaul.
Currently, there is no dedicated one click function that lets you activate maintenance mode on your Jimdo website. On our blog you can find an alternative method that can be used to emulate an under construction page:
Can I temporarily set my website to be completely offline?
If you'd simply like to take your website offline, please read our help article that explains how to unpublish your website and what needs to be considered: