RubyMine / IntelliJ: How to increase UI and fonts for presentations

When giving a presentation where you do some coding, the font size you usually use is probably a bit too small and makes code hard to read for users on smaller screens or low-bandwidth connections when the image quality is lower.

Here are two solutions.

Presentation Mode

RubyMine offers a "Presentation Mode" which you can use. Simply navigate to View → Appearance → Enter Presentation Mode to enable it.
This will increase your code editor's font size as well as your UI and works nicely when sharing a single file.

However, some controls will disappear, e.g. tabs. While you can make it work using keyboard shortcuts or the main menu at the top (hidden, move your mouse pointer to the top of your display), this is annoyingly cumbersome when you want to edit multiple files or just use your IDE like you normally would.

Scale everything (new UI)

When using new UI, go to File → Settings → Appearance and set the "Zoom" option to your liking, e.g. 150%.
Everything (UI elements, UI font, editor fonts) should be scaled accordingly.

Scaling everything manually (classic UI)

You can configure RubyMine to manually scale everything.

1. Increase UI size

Navigate to Help → Custom VM Options. A file will open.
Here, simply add the ide.ui.scale option with a scaling DPI factor.

Non-HiDPI displays default to a scale of 1, HiDPI displays may be using 2 or even 3.
If you are unsure of your default scale, navigate to "Help → Find Action" and search for "Show HiDPI info" to open an info dialog.

Here is how to zoom to 150% on a non-HiDPI display:

-Dide.ui.scale=1.5

Restart RubyMine afterwards.

2. Increase UI font size

Navigate to File → Settings → Appearance → Custom Font Size.
Set a custom font size of about 150% of the default, or whatever looks nice.

3. Custom editor font size

Unless you disabled it, you may use Ctrl + mouse wheel to zoom your editor font (Editor → General → Mouse Control).
Otherwise navigate to File → Settings → Editor → Font → Size, and set a fitting size.