hello ! im learning how to convert clothing but im having an issue with my mesh. Around the sleeves and on the back of the collar i have these shiny? triangles and i dont know how to get them to match the rest of the mesh. i thought it wouldnt be such a big issue but it really bothers me in-game. is there a way to fix this ? thanks :D

From the screenshots, it looks almost like there are random sharp edges applied to the edges of those triangles. I've seen this on TS4 CC before. I have no idea why this is. lol In Edit mode in Blender, see if the edges of those are blue. That means they are marked as sharp. Select them and then under Shading/UV click "Smooth" under Edges.

I should note, this is how you'd change this in Old Blender. I don't use newer versions, but I went and looked really quickly. So if you're using modern Blender, you'd select the sharp edges then at the top panel selected edges, then "clear sharp."

If that mesh is TS4, it's because too many creators will double their meshes, and flip the UV to cover backside see thru, similar to hair. If you merge vertices, some may not merge properly and cause what you have. To check, follow the pic. That is Blender 3.6 LTS, but it should be the same from 2.80 and up.



Sometimes, IF the backside wasn't reduced for some reason, you can decrease the merge distance (be careful to not merge adjacent vertices). Then use recalculate normals outside. You might have a stray or 3 that you'll need to do manually.

Next step would be to upload the files and someone can take a look inside.

Also, what bomaye wrote can do it.

I second what ladysmoks said, but this can also simply happen if the one side doesn't have vertices that are part of the same uv island (part of mesh on uv, in this case the backside excluding the collar), and the right front) all merged, so select all what seems like one part to you (if you have ever sewn or closely looked at real life clothes; all what would be one piece of fabric after cutting, or one piece of fabric that is without seams), do this with m --> merge by distance, and then click alt + n --> normals --> face area

Thank you! i have selected the mesh and checked the faces and i think this means they are all facing the correct way ?

thank you this worked! i unmarked the seams as sharp as bomaye suggested and followed your steps and my mesh is now smooth ! :D

Yes, your normals are good, and as you wrote, the issue is the sharps. However, unmarking all sharps will also cause visual issues. You can use Select> Select Sharp Edges, and adjust the angle. It's almost never perfect, and you will then need to manually add and remove sharps as necessary.

Even as normals direction wasn't the issue this time, I will say that I always check, since learning of this.