I couldn’t fix the issue with the GLB file, but I finally managed to solve it. I had no problem importing the FBX without the armature, but when the armature was included, it caused issues, and thats why I never reflected about polycount.
My model originally had around 9 million polys, and it seems Unreal couldn’t handle that with an armature attached, or perhaps it was too much for my PC. I attempted to remove unnecessary parts of the model, bringing it down to about 6 million faces, but that didn’t solve the problem.
However, last night I noticed that the rims alone were approximately 1.6 million polygons each. I found another pair on Sketchfab with only 120k faces, so I used them, and voila, it worked!
A big thanks for your involvement in trying to resolve my issue!