How can I delete the Windows 11 operating system from my laptop, which has a dual boot system?

Delete windows partition with your preferred tool and update-grub should remove the item from boot menu. Then, depending on your partitioning schema, you can either create a new partition in the empty space and mount it however you like or expand your existing linux partition, but options there depend on how your partitioning has been originally built and if you can leverage things like LVM or ZFS when expanding the usable storage.

And, while pretty obvious, make sure to only delete the correct partition and all data stored on that will be lost, so make sure you don't have anything important on windows side of things.