Even if the core was supported just fine, all of the IO mux stuff is pretty much guaranteed to be different even with the same chip in a different package.
I worked on a project porting from an STM32L073 to a STM32U073, which management were assured was a complete drop in replacement. Well, it was only in the sense that you could drop one onto the old PCB. It became a running joke how many software compatibilities we ran into. My favourite was an "LCD clock disable" bit became "LCD clock enable". And this was for a specifically chip designed to be an easy replacement.