Windows Boot Manager still present even after removing Windows 10

I had originally installed Windows 10 on my PC on SSD. Then I decided to dual boot Ubuntu alongside but on HDD. The grub was installed on the HDD, hence to see the GRUB menu, I had to select HDD (named as Ubuntu in BIOS, and SSD was named Windows Boot Manager) in the boot priority.

Now I installed Ubuntu on SSD and formatted the SSD while installing. I was expecting to get rid of Windows. But in the BIOS, the SSD is still named as Windows Boot Manager instead of Ubuntu, and when SSD is selected first in boot priority, it opens recovery mode. I see GRUB only when I HDD is placed first in the boot priority.

So, how do I remove the Windows Boot Manager from SSD, and make It Ubuntu. So that when I select SSD first in Boot priority, it directly boots into Ubuntu without opening the grub.

Boot priority:

Windows Error Recovery Mode:

Grub boot menu:

The output of sudo os-prober :

/dev/sdb2@/EFI/Microsoft/Boot/bootmgfw.efi:Windows Boot Manager:Windows:efi
/dev/sdb3:Ubuntu 20.04 LTS (20.04):Ubuntu:linux
/dev/sdb4:Pop!_OS 20.04 LTS (20.04):Pop:linux

Here the Ubuntu on the sdb3 disk is the Ubuntu installed earlier, the newer Ubuntu on SSD is not shown.

I deleted the /boot/efi/EFI/Microsoft/, now the Windows Boot Manager has been removed, but the SSD is not available to boot into directly.

New boot priority options:

I wanted to get rid of the Windows Boot Manager, which I did by removing the/boot/efi/EFI/Microsoft/ folder.

When I was using Windows, I could select SSD or HDD the first option in boot priority. When I selected SSD which had Windows 10 installed on it, I would boot directly to the Windows, without any GRUB prompt. But when I selected the HDD, I would get the GRUB prompt with windows, Ubuntu and Pop!_OS as the options.

Now I want to achieve similar results, just that instead of Windows, I want to use Ubuntu on the SSD. So that when SSD is selected first in the boot priority, it would boot into Ubuntu on the SSD without any GRUB prompt, but when I select the HDD first in the boot priority, I would get the GRUB prompt, to select the Ubuntu (from SSD), Ubuntu (from HDD) or Pop!_OS.

Now the problem is that I cannot see the SSD in the BIOS boot priority as seen in the 4th screen photo. Earlier I could select SSD or HDD like in the 1st screen photo. Windows Boot Manager being the SSD and the other OS being the HDD.