Error with libnftnl on Ubuntu 20.04. /usr/bin/ld: cannot find -lnftnl

I try to build a C program that uses the libnftnl library, but I get this error:

/usr/bin/ld: cannot find -lnftnl

Here is the way that I compile my code:

LIBS = -L/usr/lib/x86_64-linux-gnu/libmnl.so -L/usr/lib/x86_64-linux-gnu/libnftnl.so  -lmnl -lnftnlCFLAGS = -static -sprog:    gcc -o prog prog.c $(LIBS) $(CFLAGS)

I install:

libnftnl-dev - Development files for libnftnl
libnftnl11 - Netfilter nftables userspace API library

But I still get the same error. What am I doing wrong?