Grub bootloader missing in a dual boot setup even after reinstalling Ubuntu

I am a dual boot user, and I am facing boot issues.

Initially after setting up the dual boot, Windows did not appear in the GRUB boot menu even after enabling OS Prober. Because of this I reinstalled Windows 11, but after the reinstall GRUB disappeared completely.

I then watched several YouTube tutorials and tried fixing it by mounting the Linux partition and running grub-install. Although the installation completed successfully, my computer still booted directly into Windows.

After that I used Boot-Repair, which also reported that the repair was successful, but the system continued booting straight into Windows. Finally, I reinstalled Ubuntu, and despite the installation completing successfully, the computer still boots directly into Windows instead of showing the GRUB boot menu.