If you want to bake lightmaps, I would suggest using “smart uv project” rather than “lightmap”. Then, you can use “pack islands”, and if you use Blender 3.6 or later, you will get a pretty good packing even with the weird shapes generated by smart unwrap.
Lightmap projection separates each face individually. This would work pretty well for the more traditional use of lightmaps (old games where the environments are made of cubes), but it might leave too many seams in a more modern and high-res model.
In any case, you will have to adjust the “margin” setting when unwrapping or packing, as it controls the distance between islands.