how to delete a boot sector entry

How can I delete a boot sector entry using grub2 bootloader with Yast
I have to many sections in the menu to choose.
openSUSE Leap 15

It is not completely clear what it is that you are trying to do.

Maybe take a look at an earlier thread, and see if that is useful:

Remove Grub2 boot entry?

Yes thats what I meant.
Why is it so complicated do delete a line from the start menu. OS which is not on the system anymore can still be selected.