If you want, you can disconnect your working drive, then boot from MR USB with just second drive connected and try the MR USB - that way you don't even have to make a backup of the working drive right now.
What happens if you boot the working drive with the 2nd drive disconnected?
Do you want to keep two copies of Windows or what's your intention here? Why did you install the 2nd Windows 10?
I installed the 2nd Windows because I had an internal issue with the first. But after 1 day of searching, I figured just like 5 minutes ago what the cause of the issue is... idk maybe it's funny actually.
Anyway, I'd like to keep two installations just in case if it is possible (in case at some point something goes wrong with one of them).
The issue now is the 30 secs with black screen instead of Windows Boot Manager screen.
Problem is with Windows 10 fast startup and hibernation. On both Windows installations run
powercfg -h off
If you want to see if it will work or not, hold down the shift key when you click on shutdown from the power menu on the start menu.
You mean see whether the command would work?
Also:
I tried a normal boot now (with powering on after shutting down), and not with restarting (I only used restart previously).
When I turn off and start the laptop, I get the Windows Boot Manager with both boots (and 30 secs), and when I click on the newer installation, the laptop restarts and boots into that one while showing black screen for 30 secs as with restart (not sure about this honestly, maybe I should try multiple times and analyse).
When I click the older partition, the laptop restarts again, this time going black for just a few seconds and booting normally in Windows.
Note: while I was installing the second installation from the USB, the laptop also restarted and I the Windows Boot Manager popped up (afterwhich I chose the newer partition and the installation finished and Windows booted).
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Btw I just checked, when I press enter while the screen is black for 30 secs, the OS boots into the default OS listed first so obviously Windows Boot Manager is showing black screen instead of the interface for some reason. Maybe because of the hibernate/fast boot option.
Check the timeout in mscobfig for the second install and you will see it's less than 30 seconds.
I would disable hibernation as NavyLCDR suggested.
It's 30: https://i.snipboard.io/lFYNDV.jpg
Btw, at this point, I'd like to remove the older installation (first turn of Windows Boot Manager by turning off the timer, and then formatting the partition) and keep the new one, but I'm afraid the something would go wrong with the boot and the Windows Boot Manager.
Also, would not risk changing the hibernation settings.
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