Understanding error from ld "archive member is not mach-o or llvm bitcode file" - macos

Question

I'm getting the following error when trying to link a code on a Mac (Montery). First let me say that up until a recent upgrade to Xcode the code built fine. GCC is 10, OpenMPI and it's a Fortran code. Now there are multiple executables which build and one libaray. The library compiles fine and is archived via ar (ar -ruvs). For example, here's a compile and build line for a code.
mpif90 -O2 -g -fexternal-blas -fbacktrace -fcheck=all,no-array-temps -fallow-argument-mismatch -I../../LIBSTELL/Release -I/opt/local/include -I. -c ../Sources/boozer_coords.f
mpif90 -shared -Wl,-no_compact_unwind -O2 -g -fexternal-blas -fbacktrace -fcheck=all,no-array-temps -fallow-argument-mismatch -I../../LIBSTELL/Release -I/opt/local/include -o xbooz_xform booz_jac.o read_wout_booz.o foranl.o allocate_boozer.o transpmn.o boozer_xform.o setup_booz.o write_boozmn.o harfun.o trigfunc.o booz_params.o vcoords.o boozer.o free_mem_boozer.o boozer_coords.o booz_persistent.o ../../LIBSTELL/Release/libstell.a -L/usr/lib -L/opt/local/lib -lopenblas -lscalapack -L/opt/local/lib -lnetcdf -lnetcdff -L/opt/local/lib -lfftw3 -L/opt/local/lib -lhdf5hl_fortran -lhdf5_hl -lhdf5_fortran -lhdf5 -lz -ldl -lm
This works fine and produces an executable. However, there is another code which links to this code. For that reason archives are made of the compiled code.
mpif90 -ffree-form -ffree-line-length-none -ffixed-line-length-none -O2 -g -fexternal-blas -fbacktrace -fcheck=all,no-array-temps -fallow-argument-mismatch -I../../LIBSTELL/Release -I../../BOOTSJ/Release -I/opt/local/include -I/opt/local/include -I. -c ../Sources/thrift_main.f90
mpif90 -shared -Wl,-no_compact_unwind -O2 -g -fexternal-blas -fbacktrace -fcheck=all,no-array-temps -fallow-argument-mismatch -I../../LIBSTELL/Release -I/opt/local/include -o xthrift thrift_interface_mod.o thrift_runtime.o thrift_main.o ../../BOOTSJ/Release/libbootsj.a ../../LIBSTELL/Release/libstell.a -L/usr/lib -L/opt/local/lib -lopenblas -lscalapack -L/opt/local/lib -lnetcdf -lnetcdff -L/opt/local/lib -lfftw3 -L/opt/local/lib -lhdf5hl_fortran -lhdf5_hl -lhdf5_fortran -lhdf5 -lz -ldl -lm
ld: in ../../BOOTSJ/Release/libbootsj.a(parambs.mod), archive member 'parambs.mod' with length 2800 is not mach-o or llvm bitcode file '../../BOOTSJ/Release/libbootsj.a' for architecture x86_64
collect2: error: ld returned 1 exit status
I've had limited success trying to understand the source of this error. Here's what the table for the archive looks like.
ar -t ../BOOTSJ/Release/libbootsj.a
__.SYMDEF SORTED
SIMPUN.o
al31.o
allocate_angles.o
allocate_radial.o
bongrid.o
bootsj.o
caprsh2.o
datain.o
deallocate_all.o
denmf.o
do_fft.o
driver.o
fraction.o
grad.o
othersums.o
output.o
parambs.o
positiv.o
read_boozer.o
reorganz.o
smooth1.o
sumit.o
temp.o
tok_fraction.o
trig.o
vmec0.o
woflam.o
parambs.mod
trig.mod
vmec0.mod

Answer 1

OK so I was adding the module files (.mod) to the archive. This was incorrect. Only the Object (.o) files should be in the archive.
If I understand correctly the compiler will use the -I <path> command to look for (.mod) files. So the archive only needs the object files.