Hey, @Zafer37586609c1kv. Welcome to the Photoshop Community. I'll help you figure this out.
As a test, try using the Polygonal Lasso tool with the Shift key to draw straight lines before using backspace to erase. If that does not work, reset the Polygonal Lasso tool itself. Right-click on the P. Lasso Tool icon in the Toolbar menu and select Reset Tool.
Let me know how it goes.
Thanks!
Sameer K
(Type '@' and type my name to mention me when you reply)