Although there have been reports of "bluetooth mouse support" in iPadOS 13, it's not a feature meant for general end-user or everyday use. It's not officially stated, but apparent that Apple doesn't want everyone to be using a mouse with their iPad running iPadOS 13, else it would have been advertised in events and website.

The mouse support is enabled via one of the accessibility features, and is accessible deep within the Accessibility section of the Settings app. Here's some blog posts from popular news sites shedding some light:

• https://9to5mac.com/2019/06/19/use-mouse-with-ipad-ipados-13/

• https://www.tomsguide.com/us/ipados-mouse-support-hands-on,news-30251.html

• https://www.cnet.com/news/mouse-support-is-hidden-in-ipados-for-a-reason/

Although there have been reports of "bluetooth mouse support" in iPadOS 13, it's not a feature meant for general end-user or everyday use. It's not officially stated, but apparent that Apple doesn't want everyone to be using a mouse with their iPad running iPadOS 13, else it would have been advertised in events and website.

The mouse support is an accessibility feature and can be enabled from within the Accessibility section of the Settings app.

On your iPad (running iPadOS 13 or later), go to Settings app → Accessibility → Touch → and enable AssistiveTouch. Now, under Pointing Devices tap on Bluetooth Devices... to pair your Bluetooth mouse. (The mouse should be in pairing mode).

There is no official list of supported devices published by Apple. You will need to check yourself if your device works this way or not.