Windows 10 Boot Manager no longer a Option in System BIOS

Good Morning

Windows 10 Boot Manager:
My system use to have a SSD 250 Drive as the C:\ Running out of disk space, I purchase a 2TB SSD drive to replace the current 250GB Drive. Trying to find a way to preserve the current data and Application already installed, I unplugged the 250-SSD from the system and Installed the new 2TB-SSD. I use my ORIGINAL Windows 10 64Bit software to do a new Windows 10 installation. After installation and all the upgrade from the installed version to the latest Edition Windows 10 Pro, Version 21H1, Installed on ‎10/‎08/‎2020' OS build 19043.985
Experience Windows Feature Experience Pack 120.2212.2020.0 : I shut the system down and put my old 250-SSD drive back into the system. When I then switch my PC on the following happened:
a. The system did not boot, the message was "Please insert boot medium and hit enter to reboot."
b. When the system reboot, I pressed the Del button to enter system BIOS setting.
c. In the BIOS settings I could see my to SSD drives, selecting ANY of the two the original message appear when I exit the BIOS and restart "Please insert boot medium...."
d. I restart the PC again and this time use F12 to access the One time Boot Menu.
e. In the boot menu I could see my SSD drive and ONE BLANK OPTION.
f. Selecting this one blank option my system restart and continue to boot as normal. Selecting any of the other SSD drives result in the same error "Insert boot medium..."

Observation:
1 There is nothing wrong with my Windows 10 Pro setup because the system boot normally and work perfect.
2. The blank option manual selected does boot but cannot be booted as part of the system normal boot process. Even when it is set as the first boot option.
3. The system works normally except fot the fact that I have no Windows Boot Manager as a option in the BIOS and that I can only use the system and access the boot with the One Time Boot Menu.

Please help me to get the system back to normal WITHOUT a complete re-install. The MAIN reason for not to re-install is that I have purchase and downloaded Windows Flight simulator 2020 and that took my 5 DAYS to download without the upgrades. I really do not want to go thru that process again. The must be some PowerShell option or simple command to re-enter the Windows Boot Manager in the BIOS or fix the current BOOT option. Could the initial small portion of the installation not be isolated to run only the part where this was originally created and available in the BOOT menu?

Kind Regards
Abrie

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If you did not detach all other drives when installing Win 10 on the 2T SSD, you may have the boot manager in one drive and the OS on another. It can also be that you've installed as Legacy-MBR and the the small SSD as EFI-GPT.
Please post a Disk Manager image (full window) and expand the columns so we can read them.
How to Post a Screenshot of Disk Management

Hi Try3
I had only the one 2TB SSD drive connected to the system when I did the complete new windows 10 installation. During the installation windows did reboot many time and with no problems. Even with the upgrades after the initial install, the system rebooted several times with no problems. All this happened over a multi day sequence. I also had office 2016 installed during this period and everything run as normal. No issues at all. Multiple boot and reboot with no problem at all. I did the download of flight sim over the 5 days and during that time I only switched off the screen and switch the screen on to check on the progress of the download. After the download I could use the simulator and did multiple boots as well. The problem came when I plugged the 250GB-SSD in the system. The system restart and the Windows boot Manager was not there any more. In the BIOS I could see both the SSD drives as mentioned, but no Windows Boot Manager. On the F12 One Time Boot menu, there was now a Blank Slot with no writing or anything. I can only boot Windows 10 Pro if I select this blank slot. Any other selection resulted in a error that say " Please insert Boot media."

We need to see the screenshot of disk management.

Please post a Disk Manager image (full window) and expand the columns so we can read them.
How to Post a Screenshot of Disk Management

Here is the screen shot of Disk Manager
I have unplugged the 250 SSD and only the 2TB SSD is in the system.

Regards

- - - Updated - - -

Here is the images when I select F12 One time Boot
First is SSD select and error
Then Select blank and all is working

- - - Updated - - -

The bottom option of "P2: Samsung SSD 850 EVO 2TB" is for booting in legacy BIOS (CSM) mode and require the SSD to be MBR partitioned with a primary partition marked as Active to boot from. We need to see what format the 250 GB SSD is in - whether it is MBR with an Active partition or GPT with an EFI System Partition.

Do you want me to un-plug the 2TB drive and plug only the 250 SSD in?
Do the diskmanger screen shot again en post that information?

Regards