How to dual boot Debian 12 with existing another Linux installation by manual partitioning?

I just did that. It didn’t ask me anything about putting the Grub or anything else. I going to begin the installation. Let’s see what happens on reboot.

Update: After the installation, it showed the Grub menu like this:


But before selecting anything it booted into Fedora. Then I again restarted the PC and then it again showed the Grub menu as we expected but on entering any of the OS, it is showing the following error:

Now what to do?