Unable to use Fmt 6.1.2 with Loguru (ubuntu 20.04)

I'm trying to use loguru head with fmt 6.1.2 over an Ubuntu Focal but when I build it I get this linker error . Any CLue?

```
FAILED: src/doctestM
: && /usr/bin/c++ -fuse-ld=lld -gsplit-dwarf -O2 -g -DNDEBUG src/CMakeFiles/doctestM.dir/doctest.cc.o -o src/doctestM extern/libloguru.a extern/fmt/libfmt.a -lrt -ldl -pthread && :
ld.lld: error: undefined symbol: loguru::vlog(int, char const*, unsigned int, char const*, fmt::v6::format_args)
>>> referenced by loguru.hpp:570 (../extern/loguru/loguru.hpp:570)
>>> src/CMakeFiles/doctestM.dir/doctest.cc.o:(_DOCTEST_ANON_FUNC_6())
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
```