So I tried this mod on macOS m1 2021 pro and it doesn't seems to improve the ram usage, in fact it makes it use more ram, I don't know if that's an issue with the mods I used (conflicting with FerriteCore) or FerriteCore simply is not tested with macOS, even though it use Java (JVM) which should work cross platform for most of the code base

How are you measuring the memory usage? Are you looking at the total process memory usage or at the memory usage on the F3 screen? The first one is virtually impossible to control from within Java (the JVM tends to use as much as you allow it to use from the launcher), FerriteCore only tries to improve the second one (heap size). Note that the value in the F3 screen generally goes up for a while and then jumps back down: The value it jumps back down to is the relevant one.

that may be on FerriteCore, no way to know without a log or a list of mods.