This was Copilot's answer.

Conclusion: Enabling I2C in UIFlow2 will cause the LED matrix of the Atom Matrix to stop working because it is internally disabled. This is due to a specification (or rather a limitation) of UIFlow2.

The LED matrix (5×5 WS2812C) of the Atom Matrix is initialized by the DisplayEnable flag of M5.begin(). In the official documentation, it is written as follows:

M5.begin(true, false, true)
SerialEnable = true
I2CEnable = false
DisplayEnable = true

In UIFlow2, when using an I2C device, I2CEnable is internally set to true, and at that time, there is a behavior where DisplayEnable is automatically turned off.

This is because the internal initialization of the M5Unified series is structured in such a way that it cannot enable I2C and the LED matrix at the same time.

I want UIFlow2 to be fixed so that I can use Matrix LED and I2C at the same time.

When I tried to use the gesture unit with Atom Matrix, the matrix LED went out and it did not work.
According to Copilot, in UIFlow2, enabling I2C disables the matrix LED by design, so they cannot be used at the same time.
It seems that it's not a hardware issue, and it can be used with Arduino IDE or UIFlow1.

There are units that are only supported in UIFlow2, so I would like the limitation of not being able to use it simultaneously in UIFlow2 to be improved.