How do I get back the GRUB menu with the blue background in Debian 10?

I have a dual-boot Debian-Windows system on my computer. The partition table scheme is GPT with UEFI+Secure Boot enabled. Debian 10.10 was installed first followed by Microsoft Windows 10. I used Debian Buster's installer to create the ESP (EFI System Partition) and /boot partition. Both these partitions are not encrypted with LUKS. However, for / and swap area, they are encrypted with LUKS. Below is the layout of my partitions: 536.9MB EFI system partition formatted with FAT32 filesystem (created with Debian's installer, not encrypted) 511.7MB /boot formatted with EXT4 journaling filesystem (created with Debian's installer, not encrypted) 100GB encrypted partition formatted with EXT4 journaling filesystem (created using Debian's installer. LUKS encryption was used) 16MB Microsoft reserved area (automatically created by Microsoft Windows' installer) 100GB Microsoft Windows 10 formatted with NTFS filesystem 1. Debian Buster's 64bit installer (version 10.10) was used to create the EFI System Partition, the /boot partition and the encrypted logical volumes. Installation was successful and I was able to boot into the GRUB menu with the blue background. It had an entry named Debian GNU/Linux 2. Next I installed Microsoft Windows 10 and the installation was successful 3. I rebooted into Debian and used sudo os-prober to add the Microsoft Windows' entry to GRUB followed by sudo update-grub (After rebooting, the GRUB menu shows a Windows entry) 4. I was able to dual-boot Debian and Microsoft Windows Problem happened after I did the following: 5. With a USB stick containing Debian Testing (Bullseye), I booted into the Debian's installer screen and deleted the 100GB encrypted logical volumes. Note: I did not delete the ESP and /boot partitions. 6. As a result 100GB of free space was made available. I configured it to have two encrypted logical volumes: 99GB of the / partition, 1GB of swap area. 7. Debian Testing was installed on the 100GB partition. Installation was successful. 8. However, I am now unable to boot into the GRUB menu with the blue background. Instead all I have is a black screen with the word grub> _ (The underscore is actually the position of the cursor) Below is what I did to recover the GRUB menu with the blue background (Note: My method is destructive and I do not like it. That is why I post this advertisement to learn how to recover the GRUB menu in a non-destructive way.) 9. Booted my computer using Debian Testing installer. 10. Deleted the ESP, /boot and the 100GB encrypted partitions. 11. Re-created the ESP, /boot and the 100GB encrypted partitions. 12. Installed Debian the usual way. 13. Upon reboot, the GRUB menu with the blue background was displayed normally. The prospective freelancer should: 1. Have the technical knowledge and competence to help me solve the problem. 2. Must NOT use third-party software such as Rescatux or Super Grub Disk to solve the problem. 3. Do NOT ask me to install software from unofficial repositories. 4. Use only the commands native to Debian Buster or the Rescue Mode in Debian's installer. Desirable qualities of the prospective freelancer: 1. Patience, patience and patience. I have very limited technical knowledge and competence in Linux. 2. Should be able to write and explain the steps to solve the problem. 3. Able to communicate in written English. Fixed payment of US$40 upon successful completion of my project.