Very large file located within ~/Library/Group Containers/group.com.lminhtm.tempmonitor/db.realm I am on a Mac Mini with a 1TB SSD. After a few years my SSD is running out of space, while I keep all my user data on an external drive. My system is loaded with Multimedia Apps Photoshop, Final Cut Pro, Logic Pro X, Garage Band and many others.
When trying to find the file(s) that can be removed on the SSD, using CleanMyMac X function of Space Lens, I bump into a very large file in /Users/username/Library/Group Containers/group.com.lminhtm.tempmonitor/db.realm. This file is a whacking 378GB!
Through Google searches I can’t find any mention of this file.
Does anyone have a suggestion?
Group Containers are basically Containers, which are sandboxes for applications to store date (user data, caches, logs, etc), except the Group part means that it's at a developer level. This could be used to, for instance, keep a user logged into the same account across multiple apps made by the same developer. That said, it could be used for anything, which is what this appears to be. 

You could check with the developer, in this case: https://github.com/lminhtm. Otherwise, I'd make a backup and delete (or just move it to a different location), then test any apps you have from this developer (maybe this one?).