I don't have a Mac for testing. But I have seen similar issues on other Platforms before.
From distant memory... Try this:
When the error happens:
- Open the package DateTimeControls
- Hit the Compile button.
- Hit the Compile button, again
- Then go to the IDE menu Tools (may be preferences on Mac???) and chose "Configure Build Lazarus"
- Ensure "make clean" is not selected
- Build
It is possible you need to do this for the package DateTimeControlsDsgn ...
In the past, I have seen such errors due to a bug in fpc which did change ppu files without updating dependencies. This happened, if
- There are circular unit dependencies (within a single package, here DateTimeControls)
- There are inlined routines.
However DateTimeCtrl(Dsgn) does not seem to have this....
Make sure you only have ONE unit of that name.
E.g. if you use DateTimePicker from the Lazarus install, make sure there is no package (from OPM, or otherwise) that also has a unit of that name.
Open (both of) the package .lpk files (DateTimeControls/Dsgn) from the current install path, using "Package > Open Package".
If the IDE has an outdate path to that package (from a prior install), then this should update that.