Model modelled in blender fails in Mixamo.

I brought the game asset model from YouTube as a blender, set the helmet part to be invisible, modeled the head, neck, and shoulder, integrated the vertex group names, and pressed Ctrl + J to combine the mesh. Then I saw that the character was integrated and there was a texture in the mesh, so I exported it as an fbx file, brought it to Mixamo, and started auto-rigging. However, I was told to put on the armor-rigging marker, and there was an error, so I couldn't rig it. So I went into the edit node and clicked mesh, click M, click the button at the bottom, and it's the button to clean up lines, go back to 0.01 to clean up lines and texture nodes, check that the mesh and texture nodes are properly organized, and then I came back and started auto-riging again. But as I said before, the error went back into edit mode, exported the fbx file without texture for 4 days, exported it with texture, tried to export it with texture, tried everything you're thinking about on YouTube, Google, Chrome, on the 4th, but it didn't work because of the error, and at some point the model got twisted and eventually all the meshes on the mesh were separated, tried again and put them back together again, but it didn't work out. How many attempts did you have in 4 days? I sat in front of the computer for hours trying to fix the error, but sometimes it didn't work out and the error went on and on. What's really weird is that I didn't try this error-ridden model from the moment I took another game asset model from scratch, modeled the face, neck, and shoulder, combined it, and tried to rig it for the first time. Another really weird thing is that I have about 3 other models, and they worked out well, but despite having the exact same structure as the 3 models that used the same game asset, it was an error from the very beginning, which you think was very unsuccessful. I took a different game asset model very similar to those 3 models, modeled the 3 models and the 1 model that failed in the very same way, and even though they had the very same and identical structure, every time I tried this model, it was always me! I really want to complete this model. Please help. Please.. Please help me. If anyone can help, I would really appreciate it and help me.