Welcome, @tzhan.3, to the community!
What exactly do you want to do with a demo board?
There are currently more than 3400 different STM32 in a wide range of packaging and memory variants, so it makes no economic sense to offer a board for each of them. Instead, there are DISCOVERY, NUCLEO or EVAL boards for selected products, which can be used to start software design while your own hardware is being developed.
In your case (STM32H723 in LQFP100 with 512KB flash) I would recommend to start with the NUCLEO-H723ZG and leave out the pins that are not available later, also only use half of the flash.
Does it answer your question?
Regards
/Peter
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