Albedo is not meant for the lightmap , you assign light map to the lightmapTexture property
here is working example playground that :
- loads a glb
- loads and assigns an albedo texture
- loads and assigns a lightmap
if you open the inspector you can view the texture channels and there is a button to show the texture isolated.
The effect of the lightmap in this example is subtle but it makes a difference.
on a side note , it is possible to bake lighting into the diffuse texture , sometimes this is a viable solution and i do it myself, but you have to understand the limitations this brings. ( diffuse is not tilable when doing this for example )
Normally the lightmap texture has a much lower resolution compared to all the other channels. A little noise in this texture is even desirable 