When importing pcb files in altium designer format, release by st, (in the following links, click “STM32MP2 Series DDR memory routing guidelines examples”)
https://www.st.com/en/microcontrollers-microprocessors/stm32mp257.html#cad-resources
for example, STM32MP25XXAK_2_DDR4.PcbDoc (in STM32MP25xxAK\STM32MP25xxAK with two DDR4\CAD_Project), only three layers are annotated with asterisk in the list, I also tried to import a internal layer as the inner layer 2, but had no luck to find one.
The PcbDoc file can be opened in Altium Designer (Viewer mode), there is indeed a power plane layer. Anyone can tell me to figure out how to show up and import the power plane layer, or, all I can do is to wait for a future release to fix the problem.
Plus, My KiCAD version is 9.0.4, on Windows platform. And I start PCB Editor in standalone mode.