/3/ - 3DCG

>>999057
Shading gets weird because of incorrect normals after merging vertices. One way to fix that is with a data transfer modifier. Before merging vertices, duplicate the mesh. Merge vertices by distance on one, add a data transfer modifier to it. Set the original model as source, check Face Corner Data and click Custom Normals. Might need to change the mapping, Topology should probably work.
When working on ripped models it can be good to take these steps to clean up the model. I do it when modding games. Just be careful when merging vertices if the model has double sided or overlapping faces, such as on some skirts, capes, etc. or if the model has morphs/shape keys.
The model maker probably didn't split the UV seams, that happens when its sent to the game engine. You'll see that if you ever check vertex counts in Unity or Unreal Engine, amount will be higher than what Blender shows.