Does CubeIDE "pull-up" GPIO mode means I don't need to use external pull-up resistor?

[HTD]

That's how I would understand it. When I set the output as open drain I need an external pull-up (or pull-down) resistor. Is there a reason I SHOULD use the external resistor? If so - what does this configuration option (pull-up, pull-down) mean exactly?

[Pavel A.]

See AN4899 p. 4.3.2

https://www.st.com/resource/en/application_note/dm00315319-stm32-gpio-configuration-for-hardware-settings-and-low-power-consumption-stmicroelectronics.pdf

[Andrew Neil]

@Adam �?yskawa​ "Is there a reason I SHOULD use the external resistor?"

Anytime that the internal pullup is not suitable for your application; eg, its resistance is too high.

As the document linked by @Pavel A.​ says, the typical internal pullup value is ~ 40k - so that's going to be too much for typical I2C.