my Fenix 6x was back from service center for GPS issue (CPE missing), it works pretty well for GPS. I have OSM map for China works. when I connect Garmin Express, it always request me update for maps and I followed the procedure as requested. the whole update takes one hour plus, but at the end there is message saying storage not matching, but update fininsed.
i went to map checking whether updated maps available but nothing appear, only OSM map is there.
by the way, i copy some mp3 to music fold and it works pretty well.