I decided to start converting some clothes for the third part of the game from the fourth. And I encountered a display problem in CAS. I'm new to this, please help. How can I fix these triangular mesh displays?

Could you upload or link the .package so we can take a look?

I added files to the archive including the mesh. Thank you for helping me

Thank you

First small thing is that the feet should be removed, they aren't needed in a full body outfit and will be doubling up with the shoes.
More importantly is the UV layout, that's what is causing the strange shadowing.
Here's an example of the UVs for the base game puBodyOverallsShirt_jeans outfit:


The UV placement of the clothes should be similar to this, with the space being utilised closely matching where it is on the body. This is because all of the clothing and body textures share this space. Including the normal maps, which creates graphical oddities when they're not in the places they belong.
Here's an example of your objects UV rearranged in that way:


Note how even the orientation of the leg pieces is important, I flipped them to match the EA layout. Even if it saves space to overlap them, the lighting will mismatch.

If in doubt, check a variety of EA outfits and note where they place accessories etc.
Certain meshes will have the issue unavoidably if their UV is particularly unique, but it's important to note that this is usually only visible in CAS- it seems to be a problem with that lighting engine specifically. But it is still useful to learn how to utilise the texture space

Yes, I already figured out about the legs, because I noticed it in the game

I don't quite understand blender, could you tell me how to do the unwrapping correctly? I noticed that it is duplicated, but I don’t know how to unfold it like in your photo Initially, I used the uv from the author, I simply edited it to size for the game
I tried to use the unwrap function in the blender, but in the end the mesh was torn into small pieces. Apparently this is done completely wrong

I decided to take another mesh from another author. In blender I did not see duplicate objects in UV but the glow remains, is there no way to fix this?
Maybe I messed up with the mesh again because I made it quickly, just to test it in the game

The existing UV is usually fine, unwrapping a mesh from scratch is pretty advanced stuff as far as meshing topics go.

Here's how I separated it without unwrap:


The L key in Blender is a hotkey for Select Linked, which will highlight only the vertices connected to whatever your mouse is hovering over when pressed. Which is perfect for grabbing UVs that are overlapping with other pieces.
Once you move it somewhere easier to work with, you can mirror it by pressing S, X, then -1 (which are short cuts for Scale, X axis, by minus 100%) and click when done.

Oops, I was writing my other response and didn't see this yet

This one has the same kind of issue- all of the parts circled have their UV the same area which suggests it isn't where they should be.
I'd recommend moving those parts to the space above the arm rather than below, which seems to be the invalid location. Or squeezing them into the torso area to match their location on the mesh itself.
Note that the middle left is for parts that are in the front, middle right is parts in the back- which also plays a part in why the lighting engine trips up when they're mismatched.

For future reference it would help to open a few different types of CAS item (top, bottom, shoes, accessories- all ages should share a similar layout) and note where the UVs are placed in the square- as all of them share the same space. Especially more complicated pieces, to note where EA is putting the smaller pieces.

Thank you very much, I will try and learn!