How do I make a Windows system disk bootable?

I have created a bootable internal HDD for Windows 11 23H2 installations (in diskpart cleaned it, created a primary partition and made it active; then ran bootsect command with nt60 switch; then copied Windows ISO contents onto it).

Everything worked fine, but after installation onto a system with a new HDD with unallocated space (into that space, so that Windows creates the necessary partitions itself) that disk was not made bootable! The system requires the disk I created as an installation one for startup. The Windows directory is on the target system, however, as expected.

I tried to run bootsect in recovery command line (under Windows it gives an access error), it said it was successful, but nothing changed: I still have to keep the installation disk in the system as a second one or I get a "no bootable disk" error 😀.

Please let me know how I can make the system disk bootable (without reinstalling Windows, since there is already some software on it).

Thank you!