There's some inconsistency on the support of LPDDR2/3 on LFBGA448/LFBGA354 package.
Page 16 of the datasheet lists that LPDDR is only supported on TFBGA257/361, which is consistent with the settings in CubeMX (LFBG* packages have on LPDDR option).
However, page 10 & 11 of AN5122 STM32MP1 Series DDR memory routing guidelines clearly show that LPDDR is supported on both LFBGA packages.
I guess this is an error in the datasheet and CubeMX?
