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Hi! Certainly a simple example would be best way to get familiar with how tangent space normal maps look/ behave and to set things up in the soft that's being rendered in.

Checking the shared Painter file, it looks like the seam showing in that face area is exacerbated by seams/ discontinuity in the curvature map (and as a consequence all the masks relying on it). To check whether anything goes wrong in the layer stack, I would compare against the model with just the baked maps applied only. Only a solid fill layer with some gray and medium roughness, let the mesh maps do the rest. I think to fix, you'd need to update mesh/ UVs and re-bake or manually fix the masks.

screenshot of a mask being used, showing discontinuity at seams:


I see your also re-applying the normal map to the mesh and doing a levels on it. Here I would be careful and check if it doesn't break the shading, since the baked normal map compensates for the difference between low and high and is reliant on the lowpolys mesh shading. On the surface, just checking in Painter, looks visually okay, but would certainly preview with renderer and lighting condition that's ultimately going to be used.

Personally, I would rework the 'lowpoly', but as I understood you don't have the time to do so. Unfortunately, anything you fix with this mesh will be a band-aid, time that could go towards a better model/ UVs. If you re-work it in the future, I would look at other game meshes for reference in regards to density, topology, UVs.

The highpoly seems also more detailed than will show at the current texel density. You could add finer details during texturing, only putting silhouette defining details in the sculpt.

Good luck with the project!