Hello,
Chances are the DFU file is encrypted (although the 32h75 has a dfu boot mode) .
i would search for strings first , if you dont find any then it's a high chance the firmware file is compressed or encrypted.
with most stm's the first 8 bytes are stack and entry point so i would load a already compiled stmh75 file into ghidra so you can see what a normal compiled bin file looks like and compare the starting bytes between the two firmware files, right away it should be clear that it's encrypted/compressed or plain firmware file if it matches/dont match
darkspr1te