how repair my windows bootloader after i tried to install Kubuntu 26.04 LTS (Ubuntu flavor)

Hi. Considering that you installed Kubuntu on a second disk, I doubt that Windows was removed during the installation. But I won’t rule that out considering that there’s always a possibility that you may have installed it on the wrong disk. I’d suggest switching the boot mode back to UEFI Native (without CSM), since that may be the source of the problem. If you can boot into Windows using EFI\Microsoft\Boot\bootmgfw.efi, your Windows installation may still be intact, and you may only need to repair your boot entry. Also, considering that your laptop already had boot problems before installing Kubuntu, I’d recommend trying to figure that issue out separately.