just imho, for starters, get a real STM32 board; and chip to start with
there is a list on the stm32duino core repository
https://github.com/stm32duino/Arduino_Core_STM32
the 'preferred'' boards are like STM32F401 Nucleo or F411 Nucleo boards.
They are reasonably priced, has rather generous amount of sram and flash (compared to 'stm32f103c8 blue pills 20k sram 64k flash) and is decently fast - has the 'ART accelerator' and FPU.
The 'clone' chips are for 'advanced' users who is willing to work with possibly undocumented chips.
Technically, you would need to search or request from the APM32 manufacturer for the APM32 reference manuals and specs sheets - pinouts + all other details etc to work with APM32 chips. There is no assurance if any 'clone' chips is after all 'similar' in any way to a stm32, any 'assurance' would need to come from the APM32 manufacturer if you can even find their documents shared publicly.
There are also cases of partial documentation and many parts are undocumented, or in a worse case where documented features and functionality don't match that of a real device. Those things happens.
In all practicality, I'd guess any 3rd party can license ARM IP and design the IO extensions (e.g. gpio, uart, spi, i2c, adc etc ) and make their own ARM based microcontrollers.