Hi Ahmet, it looks like you have so-called 'double Vertices' (here: overlapping Faces).
Exaggerated, something like this, maybe:
![D-Pad.png](https://d1tq3fcx54x7ou.cloudfront.net/uploads/store/tenant_161/image/7667/image/large-28d24b706fc6c01ca3e028355372dbf3.png)
Select everything (with 'A', not with Box Select!), or the whole D pad (with Transparent Mode/X-ray vision) and the M > Merge > By Distance.