How to hide ide main window title bar? (in IntelliJ IDEA)

1. install plugin: Window Decorate Mode Switcher
2. select view->switch decorate mode

You might want to toggle the "Auto undecorate on start" option under File > Settings > Switch Decorate Mode

If you use Windows 10 or Ubuntu (tested with IntelliJ Community 2019.2 on Windows 10 and Ubuntu 20.04; for Ubuntu: thanks to the comment of @demon101)

Hide (or show) native title bar on Windows

• Open Help -> Edit Custom Options...
• Allow a personal properties file to be created
• Add a line (true = hide; false = show)

ide.win.frame.decoration=true 

• Restart IDEA

Window Decorate Mode Switcher plugin works well for me on Gnome.

This is the best solution I've found: the No Title Bar gnome extension.

Works for Linux only, but it works with ALL applications, not just those from JetBrains.

Very easy, just install the browser extension, refresh the page, click the switch to enable it, and then (optionally) remove the browser extension when you are done :) Takes effect immediately.

For macOS, Hide Title Bar plugin does the trick. It isn't perfect though, as traffic light buttons will slightly overlap the navigation bar.

It is also open source, in case anybody want to help improving it https://github.com/haringsrob/jetbrains-hide-title-bar

This issue will be resolved in 2020.03, see Option to disable merging main menu into window title

https://intellij-support.jetbrains.com/hc/en-us/community/posts/360004366159/comments/360000685899

Borderless UI can be disabled by the following steps:

1. press Ctrl+Alt+Shift+/
2. select Registry
3. switch off the ide.win.frame.decoraion key
4. restart IDE

If you use Linux:

1. Ctrl+Alt+Shift+/

2. select Registry

3. make linux.native.menu off